Code improvements Authentication/Adapter/Http

Based on https://scrutinizer-ci.com/g/Ocramius/zf2/issues/master/files/library/Zend/Authentication/Adapter/Http.php?orderField=path&order=asc

I made some improvements to the existing code. A rewrite would be better...
Please adapt the PR title to this new introduced test. Add `@group` annotations to the test docblock