Refactored TripleO jobs, e.g. to use latest openstacksdk RPM

Build and install latest RPM for openstacksdk from its master branch
instead of using the (pinned) RPM from RDO. This is necessary because
openstacksdk in RDO is currently pinned to <0.99.0 for all RDO
releases. Variable artg_change_list is used to define what code is
being build from source. The RPM of the Ansible OpenStack collection
does not have build from source because TripleO Quickstart installs
the collection from job.required-projects [1]. The latter shadows the
RPM release which is installed later by TripleO because it has a
higher precedence in ansible.cfg [2][3].

Changed the job hierarchy to other base jobs tripleo-ci-centos-8-\
standalone-build and tripleo-ci-centos-9-standalone-build. This reduces
the number of variables we have to define. It is also cleaner since our
CentOS9 job is no longer based on the CentOS8 job which prevents
issues with job variant collections due to our branched repository.

Added more Ansible modules to files which trigger TripleO jobs,
because Ansible role os_tempest [4] requires those modules and is
called in TripleO jobs. Modules which have been added include:
* openstack.cloud.compute_flavor
* openstack.cloud.image
* openstack.cloud.network
* openstack.cloud.router
* openstack.cloud.subnet

Added tripleo-ci-centos-8-standalone-osa to experimental jobs so that we
can actually run this job on demand easily.

[1] https://opendev.org/openstack/tripleo-quickstart/src/commit/cb1595223b09c991c3e8451c6d1b332a78f65a94/quickstart.sh#L123
[2] https://opendev.org/openstack/tripleo-quickstart/src/commit/cb1595223b09c991c3e8451c6d1b332a78f65a94/ansible.cfg#L19
[3] https://opendev.org/openstack/tripleo-quickstart/src/commit/cb1595223b09c991c3e8451c6d1b332a78f65a94/quickstart.sh#L595
[4] https://opendev.org/openstack/openstack-ansible-os_tempest.git

Change-Id: Ibde318678a3e44fdc297a6f29761eb0c7d77cbc9