fsck: use less aggressive method to detect mounted devices

fsck: use less aggressive method to detect mounted devices

We should not care about mountpoints in fsck if a device name
specified on command line, just check if the device is used somewhere
in /proc/self/mountinfo file.

Crazy people who use

	fsck /mountpoint

have to specify the mountpoint by the same format as in their fstab --
symlinks canonicalization is not supported.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=850965
Signed-off-by: Karel Zak <kzak@redhat.com>