Prevent printing "next step instructions" in initdb and pg_upgrade

The attached patch adds a switch --no-instructions to initdb and
pg_upgrade, which prevents them from printing instructions about how to
start the cluster (initdb) or how to analyze and delete clusters
(pg_upgrade).

The use case for this is for example the debian or redhat package wrappers.
When these commands are run under those wrappers the printed instructions
are *wrong*. It's better in that case to exclude them, and let the wrapper
be responsible for printing the correct instructions.

I went with the name --no-instructions to have the same name for both
initdb and pg_upgrade. The downside is that "no-instructions" also causes
the scripts not to be written in pg_upgrade, which arguably is a different
thing. We could go with "--no-instructions" and "--no-scripts", but that
would leave the parameters different. I also considered "--no-next-step",
but that one didn't quite have the right ring to me. I'm happy for other
suggestions on the parameter names.

-- 
 Magnus Hagander
 Me: https://www.hagander.net/ <http://www.hagander.net/>
 Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>