Fix wrong quota calculation when deleting a resizing instance

When deleting a resizing instance that has not yet finished resizing,
quotas should be adjusted for the old flavor type. Instead it
incorrectly use values from the new flavor.

This was previously fixed in bug 1099729, but has since resurfaced
with the change to use objects in delete methods.

Change-Id: I9bc68abc0d86784c642483dd0cc46c6b9c6a0c69
Closes-Bug: #1277422