Add way to group exceptions in DependencyTaskGroup

DependencyTaskGroup currently aborts execution if any exceptions are
raised.  This commit provides a way of aggregating all the exceptions
during execution and re-raising them only at the end.

blueprint stack-check

Change-Id: I6af314cc112f9286c8b38739870c6fa8b4ba9b5a
Sync resource statuses with real world resources

Attempt #2 - The Mission

This is just a work in progress to get feedback on how to go about doing
this.  This is the first step towards the auto heal/convergence
blueprint (stack-convergence).

The idea is to issue an update call with an additional flag to sync all
the resource statuses.

Once we figure out the correct way to go, this review will probably be
broken into smaller reviews.

No tests yet, just spiking.

Blueprint: stack-check
Change-Id: I4e39bfe6a3dca04305563844d5922da7e0bb67b3
wip fix the tests

Change-Id: I826cff9cbd82cc9460d09b36e3d9408805d3a2b2