Cinder backup stuck in error status

[mhg]

Brief Description
-----------------
Cinder 'backup' went into 'error' status right after being created and stayed in that status. cinder backup-show <id> shew the reason 'An unknown exception occurred'

Severity
--------
Critical

Steps to Reproduce
------------------
1 create a 'cinder backup' for a free cinder volume on a ceph lab:
cinder backup-create --container cinder --name <name> <vol_id>

Expected Behavior
------------------
The 'backup' should be created without any issue and would reach 'available' status

Actual Behavior
----------------
The 'backup' got into 'error' status right after the creation CLI executed and stayed in the states.

Reproducibility
---------------
Reproducible

System Configuration
--------------------
 storage

Branch/Pull Time/Commit
-----------------------
r/2018.10 as of 2018-10-04_01-52-00

[Ghada Khalil (gkhalil)]

Gating stx.2018.10 as this impacts functionality targeted for the October Release:
https://storyboard.openstack.org/#!/story/2003115

[Wei Zhou (wzhou007)]

Cherry-picked commit https://git.openstack.org/cgit/openstack/stx-config/commit/?id=ce5e5f8b0bc19f7f26f8bd0d8d2ea593b217ee7d from master branch to release branch r/2018.10

However this launchpad id was not specified in the commit https://git.openstack.org/cgit/openstack/stx-config/commit/?id=66afbaf4a5a24a323ac619099824cfaac0454da3

Here are the two reviews in Gerrit:

Gerrit review in master branch: https://review.openstack.org/#/c/606194/3
Gerrit review in release branch (r/2018.10): https://review.openstack.org/#/c/609052/1

[Ghada Khalil (gkhalil)]

The fix should be available in any r/2018.10 stx builds as of Oct 10/2018