Asorted quality of life improvements

I ran into some inconveniences while testing cluster-bot as deployment target.

add private.mk.example file
mark Makefile as non-parallel safe. I have MAKEFLAGS="-j $(nproc)" env var set, so make defaults to parallel make for me.
state that user must be logged into Quay to upload images
mention that Quay may create new repositories private
mention KUBECONFIG env var

freeipa / freeipa-openshift-container