add 'suppress' to PostgresNode.poll_query_until() to mute exceptions

[funbringer]

This is an alternative approach to the problem covered by PR #50.

The idea is to provide a set of suppressed exceptions to poll_query_until.

[funbringer]

@gsmol please, take a look at this one.

[codecov-io]

Codecov Report

Merging #51 into master will increase coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #51      +/-   ##
==========================================
+ Coverage   97.18%   97.31%   +0.12%     
==========================================
  Files          17       17              
  Lines        1564     1562       -2     
==========================================
  Hits         1520     1520              
+ Misses         44       42       -2

Impacted Files	Coverage Δ
tests/test_simple.py	99.81% <ø> (ø)	⬆️
testgres/__init__.py	100% <ø> (ø)	⬆️
testgres/connection.py	95.23% <100%> (+0.15%)	⬆️
testgres/node.py	97.53% <100%> (+0.46%)	⬆️

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