ZF-6428: authenticate() always fails on IBMi when using DB table-based
authentication.

Ensure that a lowercased zend_auth_credential_match element exists in
$resultIdentities array when the array is created.
Add Unit Tests specific to IBMi DB2 for CredentialTreatmentAdapter
logic.
Add TestConfiguration constants to control the unit tests.
Merge branch 'fix-6428' of https://github.com/clarkphp/zf2 into fix-6428