Preparing master to Django 3.2

[deniszh]

Removing python 2.7 from setup files and tests, testing new python and django only

(still need to actualize my master, it's severely polluted now)

[codecov-commenter]

Codecov Report

Base: 76.30% // Head: 76.28% // Decreases project coverage by -0.01% :warning:

Coverage data is based on head (89a69f3) compared to base (b52987a). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2766      +/-   ##
==========================================
- Coverage   76.30%   76.28%   -0.02%     
==========================================
  Files          88       88              
  Lines        9622     9623       +1     
  Branches     2154     2154              
==========================================
- Hits         7342     7341       -1     
- Misses       2014     2015       +1     
- Partials      266      267       +1     

Impacted Files	Coverage Δ
webapp/graphite/app_settings.py	70.96% <ø> (ø)
webapp/graphite/render/glyph.py	41.19% <100.00%> (ø)
webapp/graphite/settings.py	75.59% <100.00%> (+0.11%)	:arrow_up:
webapp/graphite/tags/redis.py	85.80% <0.00%> (-1.24%)	:arrow_down:

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[lgtm-com[bot]]

This pull request fixes 2 alerts when merging 89a69f30cd215aa24a0fdcde9c6d52e07b1616b3 into ed08fa4e2f6526ae11e55f88f70d0b6d36e4052f - view on LGTM.com

fixed alerts:

• 2 for Missing call to `__init__` during object initialization