chore: Clean up python 2 legacy

[ThosRTanner]

Fixes #788

Remove python2 specific code
Use python 3 style for constructors etc
Use python3.8 techniques in a few places

Why is this needed?

Code cleanup. This moves off deprecated python constructs (such as class X(object))

Proposed Changes

• Changes class X(object): to class X:
• changes super(Class, self) to super()
• removes the strange (python2) handling of EINTR
• removes from __future__ import absolute_import (an early python 3-ism)
• other tidyups

Does this PR introduce any breaking change?

No

Coverage changes

These appear to be because it's based on 2 commits ago on master, rather than current master. This change actually increases coverage because there's now coverage of the InterruptedException path in utils.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.46%. Comparing base (e894342) to head (075c81a).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #796      +/-   ##
==========================================
- Coverage   96.65%   95.46%   -1.19%     
==========================================
  Files          27       27              
  Lines        3554     3858     +304     
==========================================
+ Hits         3435     3683     +248     
- Misses        119      175      +56     

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