Share group types have no public extra specs

[Ben Swartzlander]

Some share group type extra specs need to be public, similarly to share type extra specs, because they affect user visible behaviors, and they would need to be preserved across migrations. For example consistent_snapshots.

It is technically possible today to create a group using a type that supports consistent snapshots, but then to later modify the group type to no longer support consistent snapshots.

[Valeriy Ponomaryov (vponomaryov)]

Partial bugfix is here: https://review.openstack.org/#/c/428748/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/428748
Committed: https://git.openstack.org/cgit/openstack/manila/commit/?id=1684b59eed9c16f1516203040364d86b475a629b
Submitter: Jenkins
Branch: master

commit 1684b59eed9c16f1516203040364d86b475a629b
Author: Valeriy Ponomaryov <email address hidden>
Date: Fri Feb 3 16:19:06 2017 +0200

    Add 'consistent_snapshot_support' attr to 'share_groups' DB model

    It will be required for support of 'consistent share group snapshots'
    feature. It is added in Ocata to ease future possible backports.
    Make it be 'Enum' with possible values 'pool', 'host' allowing to be
    nullable.

    Change-Id: I2e5984bc2fc4a487793ad8254c5dbfb0d6e33f26
    Partial-Bug: #1661266
    Partial-Bug: #1661268