Hack pg_ctl to report postmaster's exit status.

Hack pg_ctl to report postmaster's exit status.

Temporarily change pg_ctl so that the postmaster's exit status will
be printed (to the postmaster's stdout).  This is to help identify
the cause of intermittent "postmaster exited during a parallel
transaction" failures seen on a couple of buildfarm members.  This
change degrades pg_ctl's functionality in a couple of minor ways,
so we'll revert it once we've obtained the desired info.

Discussion: https://postgr.es/m/18537.1570421268@sss.pgh.pa.us