Stop attempting gsutil operation on other buckets when it succeeds
Stop attempting gsutil operation on other buckets when it succeeds

When running gsutil commands, test iterates through few telemetry buckets
attempting the operation. When the operation succeeds, there is no need to
attempt the operation on other buckets, esspecially since the further
attempts could fail if access to the buckets is not allowed.

BUG=388075

Review URL: https://codereview.chromium.org/349473002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@279421 0039d316-1c4b-4281-b951-d872f2087c98

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