pubsub: Support only string label values, cast int values to string.
pubsub: Support only string label values, cast int values to string.

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