findmnt: filter filesystems and actions for --poll

findmnt: filter filesystems and actions for --poll

The patch allows to filter by:

 * actions name:
	$ findmnt --poll=umount

 * target, source, fstype, options:
	$ findmnt --poll /mnt/test
	$ findmnt --poll -O ro
	$ findmnt --poll -t ext4

 * --first-only option to wait only for the first matching change:

	$ findmnt --poll=umount --first-only /mnt/test

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