Remove unnecessary call to fetch info_cache

The _heal_instance_info cache() always accesses instance['info_cache']
therefore we should always load the info_cache so we can avoid the extra
query to fetch it.

Closes-bug: #1309239

Conflicts:
	nova/compute/manager.py

(cherry picked from commit 5aa29b6b0a34d603e882a80cdc8e936f983b1892)

Change-Id: I3c2e005b98abf2a80276562cc05e88ba5ff199bc
Merge "Remove unnecessary call to fetch info_cache" into stable/havana