Drop rabbitmq dependency to <4.0.0

The difference in rabbit versions between openstacklib, cinder and nova
causes dependency conflicts. Version 4 of the rabbitmq module dropped
support for setting up erlang. This patch drops the required version to
between 2.0.2 and 4.0.0 in order to line up with the other modules
rather than requiring the other modules to change their dependencies as
well as set up erlang.

Change-Id: I99383b28574958a43b88b4feb0025ad795a6fda2