LinstorBaseDriver use the wrong variable when getting the device path.

[RIES Alexis]

In linstordrv driver, use the wrong variable when getting the device path.

The "backingDevice" key is used instead of "devicePath".

This error causes an error while mounting the resource on the diskless compute node, and destroys the drbd metadata on backing device when converting an image, restore backup, etc...

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/630930

[Woojay Poynter (w00jay)]

Thank you Alexis for the patch. It looks valid, but I'm awaiting on the LINSTOR CI to finish. I will post review shortly after that.

[Woojay Poynter (w00jay)]

LINSTOR CI now shows test results passing and confirms the patch working properly.
( http://us.linbit.com:8080/CI-LINSTOR/30/763/ )
Thank you for the patch.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/630930
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=64d4f717f3e898674fd248cac8876334d25dace5
Submitter: Zuul
Branch: master

commit 64d4f717f3e898674fd248cac8876334d25dace5
Author: Alexis RIES <email address hidden>
Date: Tue Jan 15 14:37:43 2019 +0100

    LinstorDrv : Fix wrong key using when getting device path.

    Using the "devicePath" key instead of "backingDevice" when getting
    the device path corresponding to the volume

    Change-Id: Id9f9c2acf0cf7ef8ebe58eeea75dc611cdce9dd1
    Closes-Bug: #1811792

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/cinder 14.0.0.0rc1 release candidate.