Relax comment sniff rules in test directories.

While its nice to have perfectly documented test cases, it is far less
important than doing that for application/library code.
Generalize the exclude-patterns.

This accounts for app/plugin dirs too.
Skip FunctionComment sniff for 3.0's test_app too.
Merge pull request #87 from cakephp/relax-test-rules

Relax comment sniff rules in test directories.