Add checkstyle testing also to tests classes in wildfly

Add checkstyle testing also to tests classes in Wildfly codebase.

Please create automated job(s) on http://ci.wildfly.org/ so we see trends in the results.
TeamCity should be able to work with Checkstyle reports using XML Report processing build feature - resources: https://confluence.jetbrains.com/display/TCD10/XML+Report+Processing and http://kalssworld.blogspot.cz/2013/03/integrating-code-quality-reports-to.html

With the checkstyle it would be great to see results per module in testsuite and maybe even per package to see the most problematic parts.

NOTE: Please add some info about and how to run checkstyle + reports into https://github.com/wildfly/wildfly/blob/master/README.md or another place you find more suitable.