Feature/auth service integration

Integration of COOPR server and External Authentication service from CDAP project. As was discussed before with @sreevatsanraman , I used dependency to the cdap repo, but in future it should be replaced with dependency to the common repo. 
Also, I copied class ```SecurityAuthenticationHttpHandler``` from the ```cdap-gateway``` package. This class also could be reused, so @sreevatsanraman , could you please move this class to the common auth service too? Then we could delete it from this repo. 
@albertshau , please take to review this PR.

It looks like ExternalAuthenticationServer has a getSocketAddress method.  You should be able to set the port to 0, let it bind to a random port, then use that method to get the port it bound to. That way we eliminate the possible of a race where something binds to the "free" port between the time that you found it and the time the server tries to bind.