Wordpress - extracted check version to module

inspired by @jvazquez-r7 I also added some wordpress specs and applied rubocop suggestions.
Also added support for a custom wp-content directory.

See #3554 for some more rspecs

Rspec Output:
![rspec](https://cloud.githubusercontent.com/assets/105281/3659872/d65abbb0-11b1-11e4-8ae8-6c286cce365d.png)

Include the exception in the message?