Add job of the same specifications as pacemaker.service (unit file)

I renamed ```pacemaker.combined.upstart.in``` to ```pacemaker.combined_extra.upstart.in``` and
added __new__ ```pacemaker.combined.upstart.in```.
I made behavior of ```pacemaker.combined```(upstart) the same as behavior of ```pacemaker.service```(systemd). That is, when pacemakerd disappeared unexpectedly, the new ```pacemaker.combined``` *respawns* it.

When this commit is not accepted, I want you to apply https://github.com/inouekazu/pacemaker/commit/bfbf425db9dc53e672bf93792c576e13d16555aa which changes the __existing__ ```pacemaker.combined.upstart.in```.