storage: add ObjectHandle.Bucket and ObjectHandle.Object methods
storage: add ObjectHandle.Bucket and ObjectHandle.Object methods

Fixes #917

Change-Id: Ie51680279cf4c9e000920772d02a25d599b31b7f
Reviewed-on: https://code-review.googlesource.com/32730
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

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