do not restrict storage driver value

[Ricardo Rocha]

Magnum restricts the possible values for the storage driver field, both in the object fields (DockerStorageDriver is an enum) and in the heat templates as a constraint.

This limits the possibility of using additional drivers in local deployments. As an example, we are interested in using the cvmfs docker graph driver (https://github.com/cvmfs/docker-graphdriver) which is compatible with overlay2, but can't easily configure it. The same is true for overlay2, which is built-in in recent Atomic versions but cannot be enabled in Magnum.

We should make the field a string and drop the constraints from the heat templates.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/510882

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/510882
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=28fff8006ae17d9afeee4ad409e12b6608fa26cb
Submitter: Zuul
Branch: master

commit 28fff8006ae17d9afeee4ad409e12b6608fa26cb
Author: Ricardo Rocha <email address hidden>
Date: Tue Oct 10 13:17:51 2017 +0000

    Make docker_storage_driver a str instead of enum

    Allow any value to be passed on the docker_storage_driver field by turning it
    into a StringField (was EnumField), and remove the constraints limiting the
    values to 'devicemapper' and 'overlay'.

    Change the docker storage setup to have a generic setup for all drivers with
    the exception of 'devicemapper', which keeps its own specific storage config
    function. For all others, do the same we already did for overlay (with two
    cases for usage of a cinder volume or not) and simply set the storage driver
    in the docker configuration to the value provided in the cluster template.

    Change-Id: I9aa8f232ce64ece4d439c0a476f463820a499617
    Closes-Bug: #1722522

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/magnum 6.0.0 release.