CI: Fix multiple failures

Tox jobs are timing out in CI due to pip dependency resolution
backtracking taking too long. When run locally, pip fails to resolve
dependencies due to upper-constraints now allowing pluggy 1.0.0 [1],
while molecule still depends on pluggy >= 0.7.1, < 1.0. See similar
tripleo bug for more details [2].

Split molecule dependencies in a separate requirements file and remove
upper constraints from its tox environment for now. As a bonus, it
should speed up execution of the jobs due to installing fewer
dependencies.

Stop using upper-constraints when installing docker python library [3].
This part of the commit can be reverted when docker 5.0.2 is in upper
constraints.

Update Kolla inventory template following renaming of haproxy role to
loadbalancer [4]. With the existing template, haproxy/keepalived
containers are not created and service deployment fails while trying to
connect to MySQL using the VIP.

[1] https://review.opendev.org/c/openstack/requirements/+/806680
[2] https://bugs.launchpad.net/tripleo/+bug/1942508
[3] https://review.opendev.org/c/openstack/kayobe/+/807128
[4] https://review.opendev.org/c/openstack/kolla-ansible/+/770618



Change-Id: I4cad83c92c32d1db2a5d3c03a78a1c533a8b9633
Co-Authored-By: Mark Goddard <mark@stackhpc.com>