Fix auto instance unrescue after poll period

We were seeing massive amounts on instance faults from failed automatic
unrescue. It was coming from the instance not having system metadata
populated.

While the route cause is a combination of using non-object instances
that were not populated with system metadata. With an object, the system
metadata would lazyload as required, but clearly not with a pure dict.

This fix ensures the non-object instance has system_metadata, so the
extraction of the flavor from the instance, during notifications sent
during unrescue, now succeed.

Closes-Bug: #1277054
Change-Id: I63bdd6c49505557829241869fd3efd2b2754530b
Merge "Fix auto instance unrescue after poll period"