Fix CI failures on Linux, Windows

[mdickinson]

This PR fixes independent CI failures on Linux and Windows

• On Windows, force use of VS 2019, to avoid a test hang due to a bluetooth-related popup from PyQt5.
• On Linux, make sure necessary libxcb-* packages are installed.

The continuous integration is unhappy again on Linux. This is a debugging PR intended to help track down what's wrong.

[mdickinson]

Relevant output:

Got keys from plugin meta data ("xcb")
QFactoryLoader::QFactoryLoader() checking directory path "/home/travis/.edm/envs/envisage-test-3.6-pyside2/bin/platforms" ...
Cannot load library /home/travis/.edm/envs/envisage-test-3.6-pyside2/lib/python3.6/site-packages/PySide2/Qt/plugins/platforms/libqxcb.so: (libxcb-icccm.so.4: cannot open shared object file: No such file or directory)
QLibraryPrivate::loadPlugin failed on "/home/travis/.edm/envs/envisage-test-3.6-pyside2/lib/python3.6/site-packages/PySide2/Qt/plugins/platforms/libqxcb.so" : "Cannot load library /home/travis/.edm/envs/envisage-test-3.6-pyside2/lib/python3.6/site-packages/PySide2/Qt/plugins/platforms/libqxcb.so: (libxcb-icccm.so.4: cannot open shared object file: No such file or directory)"
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

[mdickinson]

Adding these packages one-by-one cannot possibly be the right way to solve this problem.

[mdickinson]

Ready for review. I'm going to leave the QT_DEBUG_PLUGINS variable in, to save time next time we have to debug something similar.

[codecov-commenter]

Codecov Report

Merging #287 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #287   +/-   ##
=======================================
  Coverage   53.75%   53.75%           
=======================================
  Files         135      135           
  Lines        4394     4394           
  Branches      511      511           
=======================================
  Hits         2362     2362           
  Misses       1990     1990           
  Partials       42       42           

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[rahulporuri]

LGTM.

[rahulporuri]

FTR, looks like the package versions used in CI are - pyqt5 v 5.14.2 (edm package) and pyside2 5.15.0 (pypi wheel).