Customizing settings.xml via ENV variables doesn't work on galleon image

With released images it is possible to configure settings.xml used for S2I build via ENV variables, eg: https://github.com/jboss-openshift/cct_module/blob/1ff1d96/jboss/container/maven/api/README.adoc

If I understood correctly this was introduced/changed by CLOUD-2911. But with galleon hooked into S2I the settings.xml is replaced with the one needed for slim server so this mechanism no longer works.

This is a backward compatibility issue.