Remove network_api fallback for info_cache from APIs
Remove network_api fallback for info_cache from APIs

Fixes bug 932395

OS API and EC2 would query the network API when instance['info_cache']
had no network info.. or network info was an empty list.  The ideal was
to fall back to querying the network IP in case the cache was busted.

However, reality says this case is extremely common as it is the case
when instances are freshly built and haven't had network info assigned
yet.  The calls to network API are expensive and goes against the whole
idea of this "cache".

So, this patch removes the fallback to querying the network API.  In its
place, it adds a periodic task to the compute manager to periodically
sync the cache entry.

Since I had to fix a number of tests, I consolidated some things there
as well with regards to instance stubbing.

Change-Id: I493f811bcba4e99ac6a5756bcab473557d5c0104

n0ano/ganttclient