tests: fix move_mount test failure caused by returned error

The move_mount tests were returning -1 in case of failure causing it
to become 255 in some systems, but checktestbg in the testsuite
considers any return value greater than 128 to be a signal error.
That would cause tests that should fail to display the following test
error:
... was expected to 'fail'. Reason for failure 'killed by
signal 127'

Signed-off-by: Georgia Garcia <georgia.garcia@canonical.com>

tests/regression/apparmor/move_mount.c

@@ -240,5 +240,5 @@ int main(int argc, char *argv[])
 	}
 	if (ret == 0)
 		printf("PASS\n");
-	exit(ret);
+	exit(ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
 }