SecurityPolicyResourceHelper: Fix for command not found error when executing secedit

[39Delta]

Pull Request (PR) description

Update execution of secedit command to use full path. Issues have been seen with new server installs where the resource generates an error about not being able to find the secedit command when invoked.

This Pull Request (PR) fixes the following issues

• Fixes User Rights Assignment throwing secedit.exe error #116

Task list

• Added an entry to the change log under the Unreleased section of the file CHANGELOG.md.
  Entry should say what was changed and how that affects users (if applicable), and
  reference the issue being resolved (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 Community Testing Guidelines.
• Integration tests added/updated (where possible). See DSC Community Testing Guidelines.
• New/changed code adheres to DSC Community Style Guidelines.

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This change is