fix: expose util for rest status return

[rikatz]

Closes: #3309

Description

During the implementation of kubernetes-sigs/cluster-api-provider-vsphere#2535 we have realized it is hard to check what was the error returned from the rest/http layer of vAPI.

This PR creates a util function that can be used to check if a returned error from rest contains a specific http Status code.

Closes: #3309

Type of change

Please mark options that are relevant:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)
• This change requires a documentation update
• Build related change

How Has This Been Tested?

Extended current rest Session test to also do an invalid internal call and check the returned error

Checklist:

• My code follows the CONTRIBUTION guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

[rikatz]

Hum, this error is not related with my change

[dougm]

Thanks @rikatz , lgtm. This should also close #1639
We were thinking exposing the error type, but IsStatusError is simpler and we can revisit exposing the type later if needed.

[rikatz]

Thanks Doug, merging here