SolidFire doesn't check for empty attributes

[John Griffith]

It's possible that the attributes return in get_sf_volume during xfr/import might be empty but we're not checking that. We should be!

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/222922

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/222922
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=1c0e67996375e91878bf433877aab80d7227bf28
Submitter: Jenkins
Branch: master

commit 1c0e67996375e91878bf433877aab80d7227bf28
Author: John Griffith <email address hidden>
Date: Sun Sep 13 08:52:53 2015 -0600

    Check for empty attributes on SF volume

    This should not happen, but; we should be more strict
    about our dict reading/checking and always make sure
    the key item actually comes back and exists.

    In the case of volume['attributes'] we were always
    assuming this to be present which should be "ok", but
    it's better to verify if rather than assuming, so this
    patch adds a simple verification step before trying to
    fetch on volume['attributes'].

    Change-Id: I37a134a735aaf043aed1230d57fe458bb3a60240
    Closes-Bug: #1495247