Port clone dsc resource test improvements

[mhendric]

Pull Request (PR) description

• Ports fixes for the following issues: Issue #505 Issue #590 Changes to test helper Enter-DscResourceTestEnvironment so that it only updates DSCResource.Tests when it is longer than 120 minutes since it was last pulled. This is to improve performance of test execution and reduce the likelihood of connectivity issues caused by inability to pull DSCResource.Tests.

This Pull Request (PR) fixes the following issues

• Fixed #158

Task list

• [x] Added an entry under the Unreleased section of the change log in the README.md. Entry should say what was changed, and how that affects users (if applicable).
• [ ] Resource documentation added/updated in README.md.
• [ ] Resource parameter descriptions added/updated in README.md, schema.mof and comment-based help.
• [ ] Comment-based help added/updated.
• [ ] Localization strings added/updated in all localization files as appropriate.
• [ ] Examples appropriately added/updated.
• [x] Unit tests added/updated. See DSC Resource Testing Guidelines.
• [x] Integration tests added/updated (where possible). See DSC Resource Testing Guidelines.
• [x] New/changed code adheres to DSC Resource Style Guidelines and Best Practices.

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This change is 

[codecov-io]

Codecov Report

Merging #159 into dev will not change coverage. The diff coverage is n/a.

@@         Coverage Diff         @@
##            dev   #159   +/-   ##
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  Coverage    83%    83%           
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  Files        19     19           
  Lines      2760   2760           
  Branches      4      4           
===================================
  Hits       2303   2303           
  Misses      453    453           
  Partials      4      4

[mhendric]

Hey @PlagueHO , would you be able to review this when you get a chance? This is a direct port of your fix in XPSDesiredStateConfiguration. Thanks.