syscalls/swapon*: Cleanup.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
syscalls/swapoff*: Cleanup.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
syscalls/swapoff02: Simplify the testcase.

We don't have to create an actual swapfile to make swapoff() fail with
EPERM, any file will do.

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