Got rid of get_rootfs and set_rootfs java-like getter and
setter. Renamed rootfs to rootfs_dir to be consistent with
the name of kickstart parameter --rootfs-dir.
(From OE-Core rev: 51ec52a62ce49d1a1a83489379990f78cfe849f9)
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>