Show the rendered docker file
Show the rendered docker file

It can be quite useful (especially while debugging)
to see exactly what the final rendered Dockerfile
actually is; so when it is being rendered, log it
at DEBUG level (so that users running with DEBUG)
can see it.

Change-Id: I28b6f49a7d2f01d155f7885b6ab275c03c4e14af

GalenMa/kolla,GalenMa/kolla,stackforge/kolla,dardelean/kolla-ansible,coolsvap/kolla,rahulunair/kolla,intel-onp/kolla,dardelean/kolla-ansible,stackforge/kolla,mrangana/kolla,stackforge/kolla,nihilifer/kolla,coolsvap/kolla,dardelean/kolla-ansible,intel-onp/kolla,nihilifer/kolla,mrangana/kolla,openstack/kolla,openstack/kolla,coolsvap/kolla,rahulunair/kolla