Handle finish and revert resize notifications.

Fixes bug 1057571

Ensure that the modified instance type is reflected in the
metering data in a more timely fashion than would be allowed
by the default pollster frequency, or the cadance of the
compute.instance.exists notifications.

Change-Id: I34f01eebddfe9732d5bf69c331a0d8a63a8025ca
Merge "Handle finish and revert resize notifications."