Add optimized volume refreshes for Ceph RBD volumes

[roosterfish]

Currently only when copying Ceph RBD backed volumes for the first time the internal rbd export-diff/rbd import-diff functions are used for the transfer (local and remote).
Subsequent volume refreshes fall back to either using rsync for filesystem volumes or raw transfer in case of block volumes.

Optimized remote refreshes using the MigrateVolume()/CopyVolumeFromMigration() driver functions can be enabled by returning support for the MigrationFSType_RBD type in MigrationTypes(). It looks the necessary code from general migrations can be reused here.

Optimized local refreshes require extra work to be done in the drivers RefreshVolume() function to not fall back to the generic VFS refresh.