ensure that cpi uses the correct gem path during runtime

[fmoehler]

when executing create-env on a nix based oci image gems cannot be found.

Error message: "Cannot find [gems] in locally installed gems"

This PR fixes it.

Checklist:

Please check each of the boxes below for which you have completed the corresponding task:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• All unit tests pass locally (after my changes)
• Rubocop reports zero errors (after my changes)

Please include below the summary portions of the output from the following 2 scripts:

pushd src/bosh_azure_cpi
  bundle install
  bundle exec rake spec:unit
  bundle exec rake rubocop
popd

NOTE: Please see how to setup dev environment and run unit tests in docs/development.md.

Unit Test output:

Finished in 4.85 seconds (files took 3.43 seconds to load)
1034 examples, 0 failures

Rubocop output:

Lots of Rubocop issues in files that are not affected by this PR:

191 files inspected, 50 offenses detected, 28 offenses autocorrectable

Changelog

[jpalermo]

@fmoehler, if this is something needed for the ruby environment, is it possible to make this change in the runtime.env in the ruby release?

[fmoehler]

@jpalermo it is needed for the installation path for the gems used by the azure cpi. Something similar was done for the was cpi some time ago as well: https://github.com/cloudfoundry/bosh-aws-cpi-release/blob/master/jobs/aws_cpi/templates/cpi.erb

[jpalermo]

Yeah, I'm wondering if we should stop copy/pasting it around and put it in the ruby-release runtime.env file so when releases source that they all get the correct behavior.

Ignore me, now I understand. This needs to point to the gems in the release package, not the ruby package itself.

[klakin-pivotal]

This change looks reasonable to me.