Update prepare-commit to add Bro plugin tests

A significant amount of effort has been put into testing the bro plugin. We should update the prepare-commit script in apache/metron to support it.

https://github.com/apache/metron/commit/42068d95192e7346bf0179399193a6afe01d9925#diff-1c903f7ce0ee24ca7d4e550f9dc31cc2R342