Fix automatic confirmation of resizes for no-db-compute

compute/api.py:confirm_resize() was still making a bunch of calls
against the database that were tripping over the no-db-compute
enforcement checks. Instead of trying to unwind all of the instance
action, quota, etc code and divert to conductor, just farm out the
entire confirm_resize() call to conductor.

Fixes bug 1161402

Change-Id: I121040a3b575f5866d45cc8ef6862d67f5558715
(cherry picked from commit ec75cc2a6bc6e3f367b3377515cb9c4b99a6ab29)
Merge "Fix automatic confirmation of resizes for no-db-compute" into milestone-proposed