Add call to vol driver when accepting a transfer

Some back-ends have the notion of tenancy on volumes
and set ownership in the driver.  The update of the DB
alone when doing volume transfers isn't enough, we need
to be able to propogate the update info all the way
down to the driver level.

This patch introduces the volume api/manger/rpc calls
and implements a stub in the base driver that can
be over-ridden for those that need to take some action.

Change-Id: Ica6ae368084c44b32af5d08df14bb3745f3a37ee
Merge "Add call to vol driver when accepting a transfer"