Update retype API to use versionedobjects

Update retype API to use versionedobjects

The following patch updates retype API to use volume
versionedobjects.  Changes were made to be backwards
compatible with older RPC clients.  It only includes
changes to the core cinder code.  Changes in the
drivers are left to each driver maintainer to update.

Note that this patch DOES NOT try to use object dot
notation everywhere, since it would increase the
size of the patch.  Instead, it will be done in
subsequent patches.

Change-Id: Ie79abf085349b496930fb75a76f299e65587ba6d
Partial-Implements: blueprint cinder-objects