Fix inner has no attribute 'message'
Fix inner has no attribute 'message'

When DBDeadlock in karbor-api service, it get the following error:
AttributeError: 'DBDeadlock' object has no attribute 'message'.

This patch corrects that problem.

Change-Id: I1b268f5cca2c4efdcfb055d2fd8dfe522e6daf9d
Closes-Bug: #1891571

openstack/smaug,openstack/smaug