Add --ping as a CLI option

[offbyone]

Description

This builds in the functionality asked for in #1470; it allows pgcli to replace pg_isready from the postgresql command line toolchain

Fixes: #1470

Checklist

• I've added this contribution to the changelog.rst.
• I've added my name to the AUTHORS file (or it's already there).

• I installed pre-commit hooks (pip install pre-commit && pre-commit install), and ran black on my code.
• Please squash merge this pull request (uncheck if you'd like us to merge as multiple commits)

[j-bennet]

@offbyone This looks nice! I'd add an integration test scenario for this as well, see --list for an example:

pgcli/tests/features/basic_commands.feature

Lines 50 to 52 in 46fe654

	Scenario: list databases
	When we list databases
	then we see list of databases

[offbyone]

I added two feature tests, but one of them is failing and I don't quite know why; the exit code 0 is coming back with exit code 120, which ... I do not understand. If you know why, I'd be thrilled to update the spec.

[dbaty]

I wonder what exception we could get, here. If pgcli cannot connect to the server (or use the database), we'll fail when calling PGCLI.connect() a few blocks before, not here.

[j-bennet]

You're right, @dbaty, it's extremely unlikely, but not impossible. I've seen this once in my life, and not with postgresql; database server was up, but the transaction log was full. I'm ok with keeping the try/catch.

[dbaty]

You're right, @dbaty, it's extremely unlikely, but not impossible. I've seen this once in my life, and not with postgresql; database server was up, but the transaction log was full.

@j-bennet : then it would be useful to log the exact error we got, instead of the misleading "could not connect to the database".

[offbyone]

I am 100% fine with any of those changes; I'm not super familiar with the codebase, and it took me until earlier today to even figure out how to test it effectively. Feel free! I left "Allow edits by maintainers" enabled so you are more than welcome to push any changes that make sense to you!

[dbaty]

I added two feature tests, but one of them is failing and I don't quite know why; the exit code 0 is coming back with exit code 120, which ... I do not understand. If you know why, I'd be thrilled to update the spec.

I pulled your branch, ran behave and did not get any error. Could you clarify which command you run and the error you get?

[offbyone]

I don't, any more; I found the cause of my failure to write the tests correctly and pushed an update to it.

[j-bennet]

Looks good @offbyone; merging. 🍒 Thanks for your help, @dbaty!

[offbyone]

Thanks to all of you for the cleanups and finalizing it!