Make the base container more configurable

There is some inconsistency with the way we support custom repos. For non source builds there is no way to completely customize the Mariadb, Kibana, Elastic search, and Percona repos since they are hard coded into the Dockerfile with gpg keys. You would have to change the .repo files and change the hard coded gpg keys in the Dockerfile.

This change won't fit into current custom repo setup because these repos need to be present for source and the custom repo stuff is meant for non source.

We either expect the operator to modify the dockerfile when they need to change a repo or we integrate into the kolla-build.conf along side the current custom repo work.