Object-ify build_and_run_instance

The code for build_and_run_instance was put in place before the switch
to using Instance objects.  This updates the new boot process code to
use objects rather than dictionaries for instances.

bp remove-cast-to-schedule-run-instance

Change-Id: I47866536e924510d0d89d24336e0b690733c19e1
Merge "Object-ify build_and_run_instance"