Ignore AttributeError for instance provider
Ignore AttributeError for instance provider

Without instance provider of configuration, astara-ctl browse
will raise AttributeError, we should ignore it.

Change-Id: Iafb1513a0b6988aed75c06e10485cb5dae84ef04

stackforge/akanda-rug,openstack/akanda-rug,openstack/akanda-rug,stackforge/akanda-rug