IAP host shouldn't be restricted to a cloud endpoint url

[andrewsmartin]

In 8d5ec83#diff-1f65a44a2187458da0f00e0ebbe730e5R142-R145, the logic for self._is_iap_host uses a regex to ensure that the host name is of the form https://<deployment>.endpoints.<project>.cloud.goog/pipeline. This breaks for us, because we use a different hostname, and thus when trying to connect via IAP an auth token is not generated.

We are able to workaround this by overriding the client and def _is_iap_host(self, host, client_id), but just wanted to raise this issue here.

[jlewi]

/cc @IronPan @jessiezcc

[chensun]

/cc @chensun

[james-jwu]

Assigning to Renmin for triage

[chensun]

/assign @chensun

[chensun]

/unassign @rmgogogo