Fix issue 464

[lrk]

My proposal to fix issue #464

I renamed all role internal vars with double underscore prefix, and set values in defaults/main.yml.
I also remove unnecessary version specific files as they all contain same values that is now set as default.

I didn't come with an elegant solution for default postgis dependencies so i create the postgresql_ext_postgis_default_deps list that is used when __postgresql_ext_postgis_deps will be undefined.

side note: i think that comment with ">= version number" are incorrect, they should be "<= version number" in most cases as i think it should be read as: "when current version <= version number ..."
(example: the postgresql_jit variable comment)

I had to set login_unix_socket and --host parameters to tasks connecting to server for admin purposes to fix connection errors too

[lrk]

It seem the build fail for ubuntu / debian, i'll check that tonight.

[gclough]

Hi @lrk , there is some good stuff in here, thanks. As the build is failing, and to make it easier to review. Would it be possible to break them down into a couple of PR's?

[lrk]

@gclough sure, all i need is some time to re-work on that.

I did some other modification in my fork project for which i have to create PR here.

[thbar]

I would love to see some progress on this one. I believe #464 is the most problematic part of this role right now, because it makes it hard to override bogus defaults, such as #489 or similar (if I understand the problem correctly!).

Happy to help out a bit here (testing etc), at least on Ubuntu 16/18/20.