This commit will:
* remove old bash code common to all backends;
* create a new do_rootfs() python function that will use the new
rootfs/image creation routines;
* allow creation of dpkg based images;
* fail for rpm/opkg (not implemented yet);
(From OE-Core rev: a83144bac8d67704ff66f5dc0fc56f5b63979694)
Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>