lib: Remove unused mount_utils.c

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
lib/tst_sig: Fix fork_flag.

I've removed wrong the fork_flag check in commit:

 commit 1dbf0b4a70c0ef7c849a0b3cd42da2c3874f9432
 Author: Cyril Hrubis <chrubis@suse.cz>
 Date:   Tue Jun 10 13:49:05 2014 +0200

     lib: Remove -c option and STD_COPIES

     Remove -c option that was never working correctly.

This commit reinstates back the check that should have stayed there
and fixes all testcases that forks children.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>