swapon: -a has to complain, fix leaks

swapon: -a has to complain, fix leaks

The "swapon -a" command (without "-e" option) has to complain always
when LABEL or UUID does not exist.

Test:

	# grep foo /etc/fstab
	LABEL=foo swap swap defaults 0 0

   Old version:

	# swapon -a; echo $?
	0

   Fixed version:

	# swapon -a; echo $?
	swapon: cannot find the device for LABEL=foo
	255

	# swapon -a -e; echo $?
	0

This version also fix two memory leaks.

Signed-off-by: Karel Zak <kzak@redhat.com>