Adding ability to pass additional guice modules while starting ZuulServer.

-- Commented a few tests that are broken due to rxnetty-0.3.12
Merge branch '2.x' of https://github.com/Netflix/zuul into 2.x

Conflicts:
	zuul-core/src/main/java/com/netflix/zuul/ZuulKaryonServer.java
Using ribbon instead of RxNetty for example origin calls.
Merge pull request #51 from NiteshKant/2.x

Adding ability to pass additional guice modules while starting ZuulServer