fix regression from PR #500

[PetrDlouhy]

Fix regression introduced in #500.

Description

All the changes of test_view_login.py were wrong and they are reverted.
We are now detecting if OTPRequiredMixin is used for next URL and only then we redirect to OTP setup page.
The newly introduced test in OTPRequiredMixinTest is not changed and passes.

Motivation and Context

Fix regression described in #499

How Has This Been Tested?

• TOX tests
• tests of Login view on my own project that were not passing after Enforcing a redirect to setup of otp device when none available for user #500

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[PetrDlouhy]

I see, that now it doesn't count with non-class based views. I must fix that.

[PetrDlouhy]

I added fix for non-class based views with test.

[claudep]

Hi @PetrDlouhy, could you please fix the flake8 failure?

[codecov]

Codecov Report

Merging #558 (988e2ec) into master (0c31bbf) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #558      +/-   ##
==========================================
- Coverage   95.67%   95.66%   -0.02%     
==========================================
  Files          65       65              
  Lines        2938     2952      +14     
  Branches      329      331       +2     
==========================================
+ Hits         2811     2824      +13     
  Misses        103      103              
- Partials       24       25       +1     

Impacted Files	Coverage Δ
tests/test_views_login.py	100.00% <100.00%> (ø)
two_factor/views/core.py	96.61% <100.00%> (-0.22%)	⬇️
two_factor/views/mixins.py	100.00% <100.00%> (ø)

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[claudep]

Thanks!