Add support for CentOS

[Victoria Martinez de la Cruz]

Right now we can only create Ubuntu images, both Trusty or Xenial. It would be nice to have the option to build CentOS based images. For this purpose, we need to:

- Add elements for CentOS for each of the protocols we have
- Add the option to pick CentOS as a distro

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/450458

[Valeriy Ponomaryov (vponomaryov)]

Why do you track it as bug? It is feature request.

[Victoria Martinez de la Cruz (vkmc)]

Because there is no blueprint tracker on manila-image-elements, shall we move this to manila?

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/450458
Committed: https://git.openstack.org/cgit/openstack/manila-image-elements/commit/?id=375ddd1e9e9189c9d1dc4ababd22a78554107d9b
Submitter: Jenkins
Branch: master

commit 375ddd1e9e9189c9d1dc4ababd22a78554107d9b
Author: Victoria Martinez de la Cruz <email address hidden>
Date: Mon Mar 27 22:17:01 2017 +0000

    Add support for CentOS

    This change aims to add the foundations for CentOS support
    on manila-image-elements.

    In this patch-set, the following has been modified

    - Added elements for manila-centos-minimal
    - Added elements for centos-nfs
    - Added elements for centos-cifs
    - Renamed all elements for the different protocols to distro-protocol
    to facilitate automation
    - Modified the main script to take the distro param

    Follow-up patches will add centos-based elements
    for all other protocols supported.

    Change-Id: Ie1469a8b3973b9a15c3fa27688df3b7e7e8da688
    Partial-Bug: #1675538