This introduces some code in tests for performing live tests of the
installer across all supported Linux distributions.
A docker-compose.yaml is responsible for launching some Docker
infrastructure for package caching, which is strongly encouraged for
tests. A rbinstall-test.ini should then be generated from
rbinstall-test.ini.tmpl to specify the cache addresses, and optionally
RHEL license information.
run-install-tests.py can then be used to perform the tests. This will,
by default, run through every supported Linux distribution sequentially.
It can instead run subsets, and can run tests in parallel.
Log information will be output to logs/, to aid debugging.
