Fix on_connect multiple call on acquire

[aaliddell]

Fixes #551

The Pool on_connect handler is now called exactly once per connection, rather than on every call to acquire

Also, some things on your PR template checklist can't be done, as you don't have a CONTRIBUTORS.txt or a CHANGES folder?

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
• Add a new news fragment into the CHANGES folder

[codecov]

Codecov Report

Merging #552 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #552      +/-   ##
==========================================
+ Coverage   94.35%   94.36%   +<.01%     
==========================================
  Files          27       27              
  Lines        3740     3744       +4     
  Branches      171      172       +1     
==========================================
+ Hits         3529     3533       +4     
  Misses        179      179              
  Partials       32       32

Impacted Files	Coverage Δ
tests/test_pool.py	99.75% <100%> (ø)	⬆️
aiopg/pool.py	100% <100%> (ø)	⬆️

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[brianmaissy]

+1 on this, can we get it merged?

[oleksandr-kuzmenko]

Can you please merge this patch? PR is small and has test 👍

cc @asvetlov @popravich @vir-mir (based on MAINTAINERS.txt)

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[aaliddell]

Is this fix actually going to be considered for merge if I go through the CLA process?

[Pliner]

Hi @aaliddell,

Thanks for the contribution.