test: reinstate checks and updates integration test
test: reinstate checks and updates integration test

Re-enable two disabled checks due to differences in GCP and InProcess.
No such differences exist anymore.

Remove usage of string.Contains for testing errors in favor of
errors.Match.

Removed a redudant and long forgotten (and disabled) test.

TODO: change test "kind" from GCP to Server or DirServer.

Integration tests pass.
No lint or vet errors.

Change-Id: I3577d785f07658796dad80356cf8db1ade4c27d6
Reviewed-on: https://upspin-review.googlesource.com/4741
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@google.com>

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