nova rbd driver features are hard-coded, it should be readable from ceph.conf

[Vikhyat Umrao]

In nova rbd driver rbd features are hard-coded.

                rbd.RBD().clone(src_client.ioctx,
                                     image.encode('utf-8'),
                                     snapshot.encode('utf-8'),
                                     dest_client.ioctx,
                                     dest_name,
                                     features=rbd.RBD_FEATURE_LAYERING)

If We see above given code we are just using RBD_FEATURE_LAYERING directly.
This restrict users to use only hard-coded RBD_FEATURE_LAYERING feature.

We should give a fix which should allow users to opt in to upcoming features that have not yet become default and users can specify features in ceph.conf and nova can read features information from ceph.conf.

Fix should be something like :

Rreading rbd_default_features from ceph.conf for rbd
features configuration, falling back to layering if nothing is found.

[Vikhyat Umrao (vumrao)]

Patch is in review:
https://review.openstack.org/#/c/186537/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/186537
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=fb3713ae0ebbe030586c00b4d17bff371215e831
Submitter: Jenkins
Branch: master

commit fb3713ae0ebbe030586c00b4d17bff371215e831
Author: Vikhyat Umrao <email address hidden>
Date: Fri May 29 00:46:32 2015 +0530

    RBD: Reading rbd_default_features from ceph.conf

    This patch enables reading rbd_default_features from ceph.conf for rbd
    features configuration, falling back to layering if nothing is found.

    Closes-Bug: #1480129

    Change-Id: I639f06d6375201bdf5d469953bd80644ef433c87