Add unit tests for utils.run_shell_command

[elebow]

Description of proposed changes

• Add unit test coverage to utils.run_shell_command.
• Use fstrings in utils.run_shell_command, now that Python 3.6 is the minimum supported version.

Related issue(s)

nope

Testing

yep

[codecov]

Codecov Report

Merging #513 into master will increase coverage by 0.32%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #513      +/-   ##
==========================================
+ Coverage   18.65%   18.98%   +0.32%     
==========================================
  Files          31       31              
  Lines        5061     5063       +2     
  Branches     1282     1282              
==========================================
+ Hits          944      961      +17     
+ Misses       4090     4077      -13     
+ Partials       27       25       -2     

Impacted Files	Coverage Δ
augur/utils.py	26.72% <100.00%> (+3.81%)	⬆️

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[elebow]

I don't love the way these tests shook out, but I would plan to break utils.run_shell_command into a new class in utils/shell_command_runner.py. The main purpose of these tests is to provide confidence during that refactoring.

[elebow]

This is obsoleted by #526, but may still have value if this is ready for merging first.

[huddlej]

Closing this PR since it was superseded by #526 and #577.