bigtable: Add admin integration test.
bigtable: Add admin integration test.

Change-Id: I710be1bddab75814df1ce79feaa7bfac67cbb6a6

roth1002/gcloud-golang,hsinhoyeh/gcloud-golang,ptomasroos/gcloud-golang,googleapis/google-cloud-go,michael-grosshans/google-cloud-go,googleapis/google-cloud-go,roth1002/gcloud-golang,googleapis/google-cloud-go,Maksadbek/gcloud-golang,michael-grosshans/google-cloud-go,blowmage/gcloud-golang,hsinhoyeh/gcloud-golang,Maksadbek/gcloud-golang,blowmage/gcloud-golang,googleapis/google-cloud-go,ptomasroos/gcloud-golang