OSC server event is similar to nova's instance action commands.
Server event is the event record that had been done on a server,
include: event type(create, delete, reboot and so on),
event result(success, error), start time, finish time and so on.
These are important information for server maintains.
Change-Id: I8111091f46a0d2755728d8f9d43cc0dfe8842d13
Closes-Bug: #1642030