Allow fetching plugins as part of the build

[OpenStack Infra]

https://review.openstack.org/246942
\Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
Your project "openstack/kolla" is set up so that we directly report the documentation bugs against it. If this needs changing, the docimpact-group option needs to be added for the project. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit 2581e3099c14640a860c318aa3c49fa63d32adc6
Author: Paul Bourke <email address hidden>
Date: Fri Nov 20 11:18:41 2015 +0000

    Allow fetching plugins as part of the build

    This change allows additional archives to be fetched as part of the
    build and added to images.

    An example use case is the installation of plugins for neutron. For
    example, to add the networking-arista plugin to neutron-server, one
    would do the following in kolla-build.conf:

    [neutron-server-plugin-networking-arista]
    type = url
    location = http://tarballs.openstack.org/networking-arista/networking-arista-master.tar.gz

    The format for plugin sections is <image-name>-plugin-<plugin-name>

    The required Dockerfile additions will be added in the next patchset.

    Background to this change:
    https://review.openstack.org/#/c/207545/3/docker_templates/neutron/neutron-server/Dockerfile.j2

    Related: blueprint neutron-third-party-plugins
    DocImpact
    Change-Id: Idec2ca9fd06163c7d820e8c4bc9ebca8d9673856

[Steven Dake (sdake)]

This should be a blueprint not a bug. Please file a blueprint and we it will be prioritized approprately for newton. FWIW this is a critical item from my perspective for newton. For the moment since this is not a bug but a feature request, marking invalid.