Rabbitmq: refactor Dockerfile.j2 file
Rabbitmq: refactor Dockerfile.j2 file

install_packages macro is used 3 times instead of 1, we could simplify
code.

Change-Id: I00311e2aa3db0e53adb32a1adae85c3af2ac40fe

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