Prevent printing "next step instructions" in initdb and 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.

--