bitbake: Always use separate process for PR Service

Using the threading module interacts badly with multiprocessing used elsewhere
in bitbake under certain machine loads. This was leading to bitbake hanging on
Ctrl+C when the PR Server was being used.

This patch converts it to always use the daemonize code which
then means the threading code isn't required.

[YOCTO #3742]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
prserv/serv.py: Fix logging in daemon mode

In deamon mode we need to ensure the logging module is sending log data to the
log file. These changes ensure this happens correctly.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
world-image: add extra target

* similar to world target, but collects all PACKAGES
* recipes marked with EXCLUDE_FROM_WORLD are excluded from world as well
  as world-image
* recipes marked with EXCLUDE_FROM_WORLD_IMAGE are excluded completely
  from world-image, sometimes you can build 2 recipes in same sysroot,
  but cannot install them in the same image
* PACKAGES listed in EXCLUDE_PACKAGES_FROM_WORLD_IMAGE are also
  excluded. You can remove e.g. ${PN}-dbg, but keep all other PACKAGES.

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>