Remove conductor usage from compute.utils.EventReporter

This makes compute.utils.EventReporter use the InstanceActionEvent
object instead of making raw conductor calls. Callers are changed to
stop passing conductor API to it.

In addition, moves helper methods pack_action_event*() from
compute.utils to objects.instance_action like previously was done
with pack_action_[start|finish]().

Related to blueprint compute-manager-objects-juno

Change-Id: I308959a1b206899369a10d391991124ef014c89f
Merge "Remove conductor usage from compute.utils.EventReporter"