JVMCBC-56: Upgrade RxJava to 1.0.0 RC9

Motivation
----------
In order to get RxJava closer to 1.0.0 GA, this upgrade makes sure
we are at the latest version available.

Modifications
-------------
The dependency was upgraded and both unit and integration tests
were run to make sure no existing functionality is broken.

Result
------
We are getting one of our core dependencies closer to 1.0.0 GA

Change-Id: Id04e1aa4be6864bd9d4a77335628ee9c473df3ff
Reviewed-on: http://review.couchbase.org/42701
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Reviewed-by: Simon Baslé <simon@couchbase.com>