show: Print filelocks.img pids as %u

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
locks: Dump virtual pid of a lock owner

If we're dumping namespaced tasks, the fl_owner value we see
are the real pids of tasks, while we need virtual ones.

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