use added paths when checking ptvsd version / availabilty

[IanMatthewHuff]

For #6907

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
• Has sufficient logging.
• Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• Test plan is updated as appropriate
• package-lock.json has been regenerated by running npm install (if dependencies have changed)
• The wiki is updated with any design decisions/details.

[IanMatthewHuff]

Tested with a new environment with no debugger installed. VSCode installed debugger was correctly picked up, debugging worked, and after run ptvsd was not installed into that environment.

[codecov-io]

Codecov Report

Merging #7220 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #7220      +/-   ##
=========================================
- Coverage   58.55%   58.5%   -0.06%     
=========================================
  Files         486     486              
  Lines       21460   21460              
  Branches     3463    3463              
=========================================
- Hits        12566   12555      -11     
- Misses       8116    8129      +13     
+ Partials      778     776       -2

Impacted Files	Coverage Δ
src/client/common/logger.ts	68.55% <0%> (-6.92%)	⬇️

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