This revemos the deprecated options rabbit_host,
rabbit_hosts and rabbit_port params in the
trove::guestagent class.
Changes the guestagent config file to use the
transport_url instead of the rabbit options. [1]
[1] https://review.openstack.org/#/c/609981/
Change-Id: I2f102eb15fe59459ab1eed2e4cf87ad3c54d5c78