Add MSFT_xBLBitlocker Unit Tests

[mhendric]

Pull Request (PR) description

Add MSFT_xBLBitlocker Unit Tests

Task list

• 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.
• Unit tests added/updated. See DSC Resource Testing Guidelines.
• Integration tests added/updated (where possible). See DSC Resource Testing Guidelines.
• New/changed code adheres to DSC Resource Style Guidelines and Best Practices.

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This change is 

[codecov-io]

Codecov Report

Merging #38 into dev will increase coverage by 12.5%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             dev    #38      +/-   ##
=======================================
+ Coverage   87.5%   100%   +12.5%     
=======================================
  Files          3      3              
  Lines         96     96              
=======================================
+ Hits          84     96      +12     
+ Misses        12      0      -12

Impacted Files	Coverage Δ
...Resources/MSFT_xBLBitlocker/MSFT_xBLBitlocker.psm1	100% <0%> (+92.3%)	⬆️

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