Allow upgrade from Grizzly with ThinLVMVolumeDriver

In Grizzly, LVM thin provisioning was used by setting
volume_driver=...ThinLVMVolumeDriver.  In Havana this
functionality has moved under the standard LVM driver
with the option "lvm_type=thin" used to enable it.

We should account for the old volume_driver class path
so that the volume service behaves as expected for users
upgrading from Grizzly ThinLVM configurations.

Closes-Bug: #1231116
Change-Id: Ic29f0e5c1036232078af5c6d83c61c75a35cccd4
Merge "Allow upgrade from Grizzly with ThinLVMVolumeDriver"