Make Container Versions Configurable

Make Container Versions Configurable

There is a global 'environment' file for docker-compose called '.env'
which sits in the same directory as the yaml file[1]. Besides a shell
environment, This is where default values passed to the docker-compose
command line can be stored.

By having container specific versions listed here users of
ci-management will have an eaiser time bringing up a matrix of
different infrastructure configurations.

[1] https://docs.docker.com/compose/environment-variables/#the-env-file

Change-Id: Ie2bd92376fa817b13f4eb1d123f9fca8e10b99a5
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>