Disk: Fix Partition MaxSize discrepency - Fixes #181

[PlagueHO]

Pull Request (PR) description

This PR introduces a workaround that fixes issue #181 where the reported maximum supported size of a partition would be approximately 1MB bigger than the actual size of the partition. As long as it is unclear why the New-Partition and Get-PartitionSupportedSize cmdlets report different data if neither Offset nor Alignment parameters are used, this workaround should remain in place.

If this is not the case, Test-TargetResource for a disk configured to use the remaining size will always return false and trigger an endless cycle of LCM runs.

This PR replaces #197.

This Pull Request (PR) fixes the following issues

• Fixes #181

Task list

• [x] Added an entry under the Unreleased section of the change log in the CHANGELOG.md. Entry should say what was changed, and how that affects users (if applicable).
• [ ] Resource documentation added/updated in README.md in the resource folder.
• [ ] Resource parameter descriptions added/updated in 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.

@johlju - would you mind reviewing when you have a moment?

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This change is 

[codecov-io]

Codecov Report

Merging #213 into dev will increase coverage by <1%. The diff coverage is 100%.

@@         Coverage Diff         @@
##           dev   #213    +/-   ##
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+ Coverage   95%    95%   +<1%     
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  Files        7      7            
  Lines      978    980     +2     
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+ Hits       937    939     +2     
  Misses      41     41