Build OS Login modules and tools with custom endpoint of metadata service

[t33m]

... for testing purpose

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[google-oss-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: t33m
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[google-oss-robot]

Hi @t33m. Thanks for your PR.

I'm waiting for a GoogleCloudPlatform member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[t33m]

@illfelder , @jaiminsh , @hopkiw , folks, plz, pay attention to this pr

[hopkiw]

/hold