Update user to sid matches to be case insensitive

User to sid matches are not finding the user if the case does not match.  For example, in AD the account is configured as myserviceaccount, but the policy_value specifies that myServiceAccount should be granted privilege rights.  myServiceAccount does not match myserviceaccount and the sid cannot be found.

With this change, both the target of the match and the test expression are converted to lowercase.