fix VM create error caused by VM image not ready

[MSSedusch]

If two VM create operations are running at the same time, one of them might fail because it tries to use a VM image that is still being created:

P1 -> check image -> does not exist -> create VM image -> wait for VM image operation to finish -> once finished VM create
P2 -> check image -> exists (in creating state from P1) -> VM create -> fails with OperationNotAllowed

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 offenses (after my changes)

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

pushd src/bosh_azure_cpi
  ./bin/test-unit
  ./bin/rubocop_check
popd

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

Unit Test output:

Finished in 9.73 seconds (files took 0.84091 seconds to load)
1030 examples, 0 failures

Coverage report generated for RSpec to /workspaces/dev_bosh-azure-cpi-release/bosh-azure-cpi-release/src/bosh_azure_cpi/coverage. 4225 / 4248 LOC (99.46%) covered.

Rubocop output:

191 files inspected, 412 offenses detected, 405 offenses autocorrectable
rubocop find some issues.

Changelog

• Fix OperationNotAllowed error

[lnguyen]

LGTM

[rkoster]

ping @selzoc

[selzoc]

👍

[rkoster]

Thanks! @MSSedusch