Add busybox_git.bb recipe so that it would be easier to hack with
busybox. Set DEFAULT_PREFERENCE to "-1" in the git recipe so that we
still use the busybox_1.21.1.bb recipe by default.
(From OE-Core rev: d290bbe6d9826fbcfa2e0a7624886284697ed7eb)
Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>