enabled_backends creates invalid service

[Alon Marx]

When the value of enabled_backends in cinder.conf starts with a comma, splitting the string to backends does not filter the empty backend at the beginning and the result is an invalid cinder-volume service that fails to start.

example:
enabled_backends = ,backend1,backend2

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/353697

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/353697
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=0d894a9e9627e05650b9b900e77ce0661cdc163c
Submitter: Jenkins
Branch: master

commit 0d894a9e9627e05650b9b900e77ce0661cdc163c
Author: Alon Marx <email address hidden>
Date: Wed Aug 10 14:58:43 2016 +0300

    Fix invalid services caused by enabled_backends

    When the value of enabled_backends in cinder.conf starts with a comma,
    splitting the string to backends does not filter the empty backend at
    the beginning and the result is an invalid cinder-volume service that
    fails to start. The same applies to enabled_backends ending with comma
    or having extra commas in the middle.

    Change-Id: Ib18d109d28d97e2d3681eff3784f08fd82bfee71
    Closes-Bug: #1611353

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/cinder 9.0.0.0rc1 release candidate.