CertReq: Expired Certificate Validation

[thesmall]

Pull Request (PR) description

Adds logic to exclude certificates which have already expired from being included in the array of certificates returned from the certificate store, when building a certificate request to be submitted to the PKI.

If the certificate request attempts to perform renewal on a certificate that has already expired, the certificate request will be denied by the Certification Authority with an error: Certificate not issued (Denied) Error Verifying Request Signature or Signing Certificate A required certificate is not within its validity period when verifying against the current system clock or the timestamp in the signed file..

This Pull Request (PR) fixes the following issues

None

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 

[PlagueHO]

Hi @thesmall - are you still working on this one?