kokoro: name build artifact after gerrit revision
kokoro: name build artifact after gerrit revision

Change-Id: Id21271920f3e18a9151a09ee69ec416e5bc565c6
Reviewed-on: https://code-review.googlesource.com/11234
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Ross Light <dfccc06f14414bff5a59be7fc90abf4404b47fc8@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go