Fix oslo.db import due to move out of the namespace package

oslo.db going to move out of the namespace package soon - see change
Ie96b482b9fbcb1d85203ad35bb65c1f43e912a44 - so we should fix related
import in Sahara to avoid of issues after the new release.

Change-Id: I967aa43f7e1c27b14439db1ab2b7f3cd0f1f9e1b
Merge "Fix oslo.db import due to move out of the namespace package"