bitbake/runqueue: make dry-run do everything except execute

bitbake/runqueue: make dry-run do everything except execute

Make dry-run do everything except executing the task, instead of
cutting it off earlier. This fully tests the code path for running the
child task (parsing and fakeroot), as well as enabling future
functionality such as using dry-run to produce signature files.

(Bitbake rev: bf1d7739618dabf3872a868230c0112b9ad2a2c0)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>