Due to some different behavior of the distributions that may be used for docker setups it was necessary to implement some checks for supervisord and its configurations

mysql 5.6 is not supported on buster

Configurable via config/config (type and version)

Re-added retry logic from qa/installer to prevent failed setups due to updated buildservice repositories while installer is preparing

in preperation for mariadb, now with configurable mysql version support (works on Debian 9/10, CentOS6/7)