Changed tests to use pytest instead of unittest.

[lizsalmon]

Description:

• After a discussion with Anish I've changed some of the unittest classes to be pytest tests and added pytest.fixtures if needed.
• There are a few changes that I am unsure of with the fixtures (specifically in test_hypervisor_state_sensor.

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Submitter:

Have you (where applicable):

• Added unit tests?
• Checked the latest commit runs on Dev?
• Updated the example config file(s) and README?

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Reviewer

Does this PR:

• Place non-StackStorm code into the lib directory?
• Have unit tests for the action/sensor and lib layers?
• Have clear and obvious action parameter names and descriptions?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.68%. Comparing base (e513a8e) to head (7a57980).
Report is 16 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #294   +/-   ##
=======================================
  Coverage   97.68%   97.68%           
=======================================
  Files         135      135           
  Lines        4875     4878    +3     
  Branches      266      265    -1     
=======================================
+ Hits         4762     4765    +3     
  Misses        102      102           
  Partials       11       11           

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