As mnt_roots always has a slash at the beginning we don't need another:

(00.156035)      1: mnt: Move the root to //tmp/.criu.mntns.ZKVJHl/15-0000000000
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>