Updated the bins_dir to default to pg_bin

[scott-w]

What does this PR do?

Updates the configuration to match the documentation. Originally the docs said postgres.pg_bin was the config to update, however the code looks at postgres.bins_dir. This PR supports both behaviours so we can transition users who need an immediate fix away from the original workaround.

I've also updated the documentation so we can be clear that the behavior is unsupported but is necessary in certain situations.

What issues does this PR fix or reference?

#37935

Previous Behavior

The system only looked in postgres.bins_dir in the configuration. The docs said to update postgres.pg_bin

New Behavior

The system defaults to look at postgres.pg_bin first, then falls back to postgres.bins_dir to prevent workarounds failing.

Tests written?

No

[gtmanfred]

Can you deprecate this using the warn_until function

https://docs.saltstack.com/en/latest/topics/development/deprecations.html

[scott-w]

@gtmanfred Yeah no worries. What version should I put in?

[gtmanfred]

I would say Oxygen.

[ticosax]

Thank for this,
Please can you rebase this pull request against 2016.11 branch ? I think, it is more a regression fix rather than a new feature. It is a blocker to upgrade saltstack on some linux distros.

[scott-w]

Hi @ticosax yeah, I'll do that now. I'll close this PR.

[ticosax]

You don't have to close it. click on EDIT button and change the base branch.

[scott-w]

Ahh yeah, I've not used this in Github before yet :P

[ticosax]

Doens't seem to work like I expected. Sorry. I'm afraid you will have to submit a new patch.

[scott-w]

@ticosax There we go, I've gotten rid of the extraneous commits from develop :)