When a non-root user runs "criu restore" and criu has the suid bit,
a process will run with non-zero uid and gid.

Before the 4.13 kernel (4d28df6152aa "prctl: Allow local CAP_SYS_ADMIN
changing exe_file"), PR_SET_MM_EXE_FILE fails if uid or gid isn't zero.
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>