pubsub: add SubscriptionInProject
pubsub: add SubscriptionInProject

Fixes #849

Change-Id: I3ed410f7b0cc2e94765a1f4672e7f65ac75dca6e
Reviewed-on: https://code-review.googlesource.com/22190
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

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