This patch add a way to choose container engine inside tool and test
scripts. This is in preparation for Podman introduction but still
leaves Docker as default container engine.

Signed-off-by: Martin Hiner <m.hiner@partner.samsung.com>
Change-Id: I395d2bdb0dfb4b325b6ad197c8893c8a0f768324

During the Train cycle, Bifrost switched to using JSON-RPC by default
for Ironic's internal communication [1], avoiding the need to install
RabbitMQ. This simplifies things, so we may as well remove our custom
configuration of RabbitMQ.

[1] https://review.openstack.org/645093

Change-Id: I3107349530aa753d68fd59baaf13eb7dd5485ae6

This change is intended to ease the addition of new test scenarios, by
splitting the existing setup_gate.sh script up into several smaller
scripts. We may wish to further break these scripts up in future,
depending on the requirements of new test jobs.

Change-Id: Ifa442ac79a54f749c56d20f5f7383c3852d95268