Remove apache rat check from main travis build and move to a sub build

Currently, when a Travis build fails, we are unable to tell if the the failure was due to the rat check failure or due to a system test failure. You have to scroll all the way to the bottom of the build output page to find out if the rat check failed.

An improvement would be to move the rat check to a sub build so that it is easy to visually identify if the build failure is due to the rat check or system test failure.