htype: Remove clean_migrated callback

With proper init_src/_dst setup we can just use the unroll_fs one.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
htype: Rename prepare_fs and unroll_fs

Mount and Umount are much more common in that context.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
ovz: Properly connect veth to bridge if required

Documented configuration is when veth is attached to a
bridge device. Keep that in mind and connect device back
into the bridge after migration.

After this bridged container can live-migrate between
two nodes and networking still works after that ;)

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>