Coverage calculation accounting for concurrency

[AnthonyHorton]

While working on #547 I ran into problems with inaccurate test coverage reports because the existing coverage and Travis CI configurations produced results which did not take into account concurrency, in particular scripts started with subprocess. I was able to come up with some changes to the configurations that appear to resolve these problems, and should properly calculate test coverage involving multiprocessing, threading and subprocess concurrency. At @wtgee's suggestion I have split these config changes out into a Pull Request of their own.

[codecov]

Codecov Report

Merging #566 into develop will increase coverage by 0.1%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           develop     #566     +/-   ##
==========================================
+ Coverage    70.44%   70.55%   +0.1%     
==========================================
  Files           64       64             
  Lines         5518     5518             
  Branches       767      767             
==========================================
+ Hits          3887     3893      +6     
+ Misses        1425     1420      -5     
+ Partials       206      205      -1

Impacted Files	Coverage Δ
pocs/camera/camera.py	90.81% <0%> (+1.08%)	⬆️
pocs/serial_handlers/protocol_arduinosimulator.py	77.3% <0%> (+1.53%)	⬆️

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[wtgee]

LGTM but was almost expecting a huge jump in coverage. :) Will be nice to be more accurate. Will leave for @jamessynge to see if he has comments.

[AnthonyHorton]

@wtgee It would make more difference if $POCS/scripts/*.py were included in the coverage calculation! Python scripts launched by tests via subprocess are properly counted with this set up, which is the main difference I was after.

[jamessynge]

I don't have an opinion yet as to how well it works, but would like to try!
I am surprised that we don't see more of a jump, but I'll take a look once merged and I can try it on my laptop.

[jamessynge]

I'm looking forward to trying this out, and hopefully getting some improved coverage.