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
Correct a PSR-2 Code Style error I had missed before issuing PR.
Reword a few comments.
Format source code to better conform to ZF2 Coding Standards:
https://zf2-docs.readthedocs.org/en/latest/ref/coding.standard.html
Merge pull request #6510 from clarkphp/fix-6428

Fix 6428 - authenticate() always fails on IBMi when using DB table-based authentication
[#6510] Fix test setup

- Moved declaration of driver options into `setUp()` so that we can know
  constants are declared before we attempt to assign their values.
Merge branch 'hotfix/6510'

Close #6510