btrfs-progs: tests: use 'btrfs check' instead of btrfsck

Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: tests: build prerequisities, btrfs-image and btrfs

Build required utilities from the main Makefile and just check in the
test scripts.

Signed-off-by: David Sterba <dsterba@suse.cz>