Added extension point

[andreasschramm]

Hi, please consider adding extension points for users.

[centos-ci]

Can one of the admins verify this patch?

[rhscl-bot]

Can one of the admins verify this patch?

[hhorak]

Thanks for the contribution, we had several discussions about how to make this generally and it currently seems like using s2i approach might be better, see #34 for more details.

[andreasschramm]

I was about to ask about that, i have seen your pull request, and agree it might be a better approach.
I have yet to find out the best way to do some other things, yum and whatever.

[hhorak]

Sorry, my previous comment mentioned #34, but I wanted to point to #32.. but you probably found the right one.. I've also added an example of a Dockerfile that changes USER and thus can install additional packages -- https://github.com/hhorak/mariadb-container/blob/s2i-support/10.1/test/Dockerfile

[andreasschramm]

thanks, i was unsure on to how to do it "the right way", dockerfile or assemble. Still finding out the best way to provide such functionality in a userfriendly way.