Make pbx_lua handle managing the autoservice better.

Make pbx_lua handle managing the autoservice better.

Make autoservice_start() and autoservice_stop() return nothing.  Also check if
the autoservice flag is set before starting or stopping the autoservice and
stop and start the autoservice when returning control to and getting control
from the pbx engine.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@317803 65c4cc65-6c06-0410-ace0-fbb531ad65f3