Fix extend_volume error handling.

If the async call to the manager/driver failed, the API still updated
the quota and volume size in the DB. Solution is to move these tasks
down to the manager, where we know if the extend succeeded.

Change-Id: I668fd659830bd6d410be64a1f5116377b08a9e96
Fixes: bug 1201814
Merge "Fix extend_volume error handling."