api_start: always close fds 0-2 when daemonized

commit 507cee3 moved the close and re-open of fds 0-2 into
do_start.  But this means that the lxc monitor itself keeps the
caller's fds 0-2 open, which is wrong for daemonized containers.

Closes #548

Reported-by: Mathieu Le Marec - Pasquet <kiorky@cryptelium.net>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>

src/lxc/lxccontainer.c

@@ -722,6 +722,12 @@ static bool do_lxcapi_start(struct lxc_container *c, int useinit, char * const a
 			return false;
 		}
 		lxc_check_inherited(conf, true, -1);
+		close(0);
+		close(1);
+		close(2);
+		open("/dev/zero", O_RDONLY);
+		open("/dev/null", O_RDWR);
+		open("/dev/null", O_RDWR);
 		setsid();
 	} else {
 		if (!am_single_threaded()) {