cloud-sql/sqlserver/mssql: should handle insert error failed

[flaky-bot]

This test failed!

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---

commit: 74ab5d7
buildURL: Build Status, Sponge
status: failed

Test output

expected 400 "Bad Request", got 500 "Internal Server Error"
Error: expected 400 "Bad Request", got 500 "Internal Server Error"
    at Test._assertStatus (node_modules/supertest/lib/test.js:268:12)
    at Test._assertFunction (node_modules/supertest/lib/test.js:283:11)
    at Test.assert (node_modules/supertest/lib/test.js:173:18)
    at localAssert (node_modules/supertest/lib/test.js:131:12)
    at /tmpfs/src/github/nodejs-docs-samples/cloud-sql/sqlserver/mssql/node_modules/supertest/lib/test.js:128:5
    at Test.Request.callback (node_modules/superagent/lib/node/index.js:728:3)
    at IncomingMessage.parser (node_modules/superagent/lib/node/index.js:916:18)
    at endReadableNT (_stream_readable.js:1145:12)
    at process._tickCallback (internal/process/next_tick.js:63:19)

[shubha-rajan]

The build is passing after merging #1783: https://fusion.corp.google.com/projectanalysis/summary/KOKORO/prod%3Acloud-devrel%2Fnodejs-docs-samples%2Fpresubmit%2Fcloudsql-sqlserver