Updates to envvars for CI build to support VSTS automation

[d3r3kk]

Extend const IS_CI_SERVER from src/test/constants.ts to include new constant IS_VSTS, represented by the environment variable TF_BUILD present on VSTS.

• Set MochaOpts.useColor=false to take into account VSTS's lack of support for this.

Helps #934

This pull request:

• Has a title summarizes what is changing
• Includes a news entry file (remember to thank yourself!)
• Works on all actively maintained versions of Python (e.g. Python 2.7 & the latest Python 3 release)
• Works on Windows 10, macOS, and Linux (e.g. considered file system case-sensitivity)

[d3r3kk]

Spawn a new build...

[codecov]

Codecov Report

Merging #1872 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1872      +/-   ##
==========================================
+ Coverage   74.44%   74.46%   +0.02%     
==========================================
  Files         282      282              
  Lines       13253    13253              
  Branches     2382     2382              
==========================================
+ Hits         9866     9869       +3     
+ Misses       3257     3253       -4     
- Partials      130      131       +1

Impacted Files	Coverage Δ
src/client/debugger/Main.ts	51.85% <0%> (-0.5%)	⬇️
src/client/debugger/mainV2.ts	79.91% <0%> (+2%)	⬆️

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[d3r3kk]

Try this out on the new CI definition in VSTS...

[d3r3kk]

Another crack at VSTS CI

[d3r3kk]

Once again...

[d3r3kk]

Once again...

[d3r3kk]

@DonJayamanne this change actually doesn't seem to have any effect at all. If you look here at the code, and then search the 'testSingleWorkspace' output for that test, you can see the IS_CI_SERVER value is being completely ignored. Perhaps this is due to a shortcoming on the VSTS side, I'll check it out further... but maybe how I've used the environment variable is to blame?

[DonJayamanne]

Agreed, something wrong in VSTS, cuz it works as expected on Travis and appveyor

[d3r3kk]

I found it. The VSTS env var TF_BUILD is set to "True" in true MSBuild style.

My expression was failing due to case mismatch!

I found that in the VSTS tooling it is enough to test for the existance of the TF_BUILD environment variable so I've decided to follow that pattern. (I doubt very much a VSTS build agent would ever define that value as "False" or anything else...).

[d3r3kk]

@DonJayamanne yep this fixes it! I'm shoving it in... will watch it and revert tonight if it turns out problematic...