feat: support apiEndpoint override in client constructor

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:9d5cae1454da64ac3a87028f8ef486b04889e351c83bb95e83b8fab3959faed0
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/cloud/kms/artman_cloudkms.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/js/kms-v1.
.eslintignore
.eslintrc.yml
.github/ISSUE_TEMPLATE/bug_report.md
.github/ISSUE_TEMPLATE/feature_request.md
.github/ISSUE_TEMPLATE/support_request.md
.jsdoc.js
.kokoro/common.cfg
.kokoro/continuous/node10/common.cfg
.kokoro/continuous/node10/docs.cfg
.kokoro/continuous/node10/lint.cfg
.kokoro/continuous/node10/samples-test.cfg
.kokoro/continuous/node10/system-test.cfg
.kokoro/continuous/node10/test.cfg
.kokoro/continuous/node11/common.cfg
.kokoro/continuous/node11/test.cfg
.kokoro/continuous/node8/common.cfg
.kokoro/continuous/node8/test.cfg
.kokoro/docs.sh
.kokoro/lint.sh
.kokoro/presubmit/node10/common.cfg
.kokoro/presubmit/node10/docs.cfg
.kokoro/presubmit/node10/lint.cfg
.kokoro/presubmit/node10/samples-test.cfg
.kokoro/presubmit/node10/system-test.cfg
.kokoro/presubmit/node10/test.cfg
.kokoro/presubmit/node11/common.cfg
.kokoro/presubmit/node11/test.cfg
.kokoro/presubmit/node8/common.cfg
.kokoro/presubmit/node8/test.cfg
.kokoro/presubmit/windows/common.cfg
.kokoro/presubmit/windows/test.cfg
.kokoro/publish.sh
.kokoro/release/docs.cfg
.kokoro/release/docs.sh
.kokoro/release/publish.cfg
.kokoro/samples-test.sh
.kokoro/system-test.sh
.kokoro/test.bat
.kokoro/test.sh
.kokoro/trampoline.sh
.nycrc
.prettierignore
.prettierrc
CODE_OF_CONDUCT.md
CONTRIBUTING.md
LICENSE
README.md
codecov.yaml
renovate.json
samples/README.md

> core-js@2.6.9 postinstall /tmpfs/src/git/autosynth/working_repo/node_modules/core-js
> node scripts/postinstall || echo "ignore"

Thank you for using core-js ( https://github.com/zloirock/core-js ) for polyfilling JavaScript standard library!

The project needs your help! Please consider supporting of core-js on Open Collective or Patreon: 
> https://opencollective.com/core-js 
> https://www.patreon.com/zloirock 

Also, the author of core-js ( https://github.com/zloirock ) is looking for a good job -)


> protobufjs@6.8.8 postinstall /tmpfs/src/git/autosynth/working_repo/node_modules/protobufjs
> node scripts/postinstall

npm notice created a lockfile as package-lock.json. You should commit this file.
added 583 packages from 859 contributors and audited 1395 packages in 12.076s
found 0 vulnerabilities


> @google-cloud/kms@1.0.0 fix /tmpfs/src/git/autosynth/working_repo
> eslint '**/*.js' --fix


/tmpfs/src/git/autosynth/working_repo/samples/addMemberToCryptoKeyPolicy.js
  26:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/addMemberToKeyRingPolicy.js
  25:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/createCryptoKey.js
  24:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/createCryptoKeyVersion.js
  24:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/createKeyring.js
  26:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/decrypt.js
  29:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/destroyCryptoKeyVersion.js
  25:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/disableCryptoKeyVersion.js
  25:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/enableCryptoKeyVersion.js
  25:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/encrypt.js
  29:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/getCryptoKey.js
  24:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/getCryptoKeyIamPolicy.js
  24:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/getKeyring.js
  23:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/getKeyringIamPolicy.js
  23:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/listCryptoKeys.js
  23:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/listCryptoKeyVersions.js
  24:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/listKeyrings.js
  25:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/quickstart.js
  22:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/removeMemberCryptoKeyPolicy.js
  26:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/removeMemberFromKeyRingPolicy.js
  25:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/restoreCryptoKeyVersion.js
  25:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/setPrimaryCryptoKeyVersion.js
  25:23  error  "@google-cloud/kms" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/system-test/kms.test.js
  19:26  error  "chai" is not found  node/no-missing-require

✖ 23 problems (23 errors, 0 warnings)

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @google-cloud/kms@1.0.0 fix: `eslint '**/*.js' --fix`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the @google-cloud/kms@1.0.0 fix script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/kbuilder/.npm/_logs/2019-06-05T14_19_24_001Z-debug.log
synthtool > Cleaned up 2 temporary directories.
synthtool > Wrote metadata to synth.metadata.

[codecov]

Codecov Report

Merging #173 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #173   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines           4      4           
=====================================
  Hits            4      4

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 553d8c7...ed1e532. Read the comment docs.