Clean dockerfile output on Ubuntu distro
Clean dockerfile output on Ubuntu distro

Ubuntu Dockerfile output actually contains not related RPM comments.

Change-Id: I306baeaa2d4ffa1269a347e1e1b23f26caefda06

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