Change the default install version of RabbitMQ Server to 3.6.1-1.
Additionally, the functional test playbook file has been split into
multiple, more focused, files. Tests to ensure that the expected version
of RabbitMQ Server is running and to upgrade from 3.5.7 to 3.6.1 have
been added.
Change-Id: I8907a3a71334be7b89ad743c3f2031e0a42a00f2