Make main thread used for common jobs

Make main thread used for common jobs

This commit make the main thread behaving
like any other threads. The main loop
is shared across threads, the first one
without job taking it. The main event loop
now have the lowest priority. It is
activated only when no job is queued.
This has the good effect to not try to
overfill the queue of jobs.

Change-Id: I07cecc9d94a02134c63bc2a814db56e171ab719e
Signed-off-by: José Bollo <jose.bollo@iot.bzh>