snapshot-rootfs.sh, vmhost-status.sh: New path for btrfs binary

snapshot-rootfs.sh, vmhost-status.sh: New path for btrfs binary

With Ubuntu 15.10, the path of the btrfs binary has changed from /sbin/btrfs to /bin/btrfs.
Therefore, I stopped referring to the binary by full path.
While /bin is in the PATH by default on Ubuntu 15.10 (even for cron jobs),
on older Ubuntus or other distros, you may possibly need to
add /sbin or /bin to the PATH for these scripts.

	modified:   fs/snapshot-rootfs.sh
	modified:   host/vmhost-status.sh