Originally we use hardcoded "build" as the default task. This commit
fixes it by using BB_DEFAULT_TASK.
This fixes [YOCTO #2283]
(Bitbake rev: 7540f8d446345559ea9b47f4ff71d203ffdfaf8d)
Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>