Fix detection of mounted filesystem.

Fix detection of mounted filesystem.

Update the way how fsadm detects mounted filesystem.
With udev /dev/dm-XXX paths are now returned - but mount or /proc/mounts
prints names in form of /dev/mapper/vg-lv - so the match was not found.
Fixex RHBZ #638050.

Current solution uses same trick as mount and detects vg-lv name through
/sys where available - this should be reasonable safe.

Instead of calling mount without parameter to get actual mount table,
switch to use /proc/mounts directly.