add test-build-tags make target

[jackfrancis]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

This PR adds a test-build-tags make target to enable us to easily validate the functionality of provider-specific build tags.

While doing this I cleaned up several issues, including some that were preventing a few providers from even compiling w/ their build tags. :/

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[jackfrancis]

/assign @MaciekPytel

[x13n]

I wonder if we could have a single source of truth for this. I thought something like:

ls cluster-autoscaler/cloudprovider/builder/ | grep -e '^builder_.*\.go' | sed 's/builder_\(.*\)\.go/\1/'

Though the downside is if the list becomes empty, the test will keep on passing. Thoughts?

[jackfrancis]

I incorporated this improvement and ensured that there are the right error paths as well, ptal. Thanks!

[jackfrancis]

/assign @BigDarkClown @feiskyer I think this and then kubernetes/test-infra#33656 would ensure that our build tags remain hygienic

cc @voelzmo

[x13n]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, x13n

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• cluster-autoscaler/OWNERS [x13n]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment