Kubernetes Informer & Added more events of Pod

[gemblerz]

For details on Kubernetes Informer, refer to #118

Changes in the scheduler-sent-events:

• "sys.scheduler.status.plugin.promoted” changed to "sys.scheduler.status.plugin.queued"
• "sys.scheduler.status.plugin.selected" is newly added to indicate that given scheduling policy selected the plugin to schedule.
• "sys.scheduler.status.plugin.scheduled" previously indicated the meaning of "sys.scheduler.status.plugin.selected", described above. It now indicates that Kubernetes created a Pod for the plugin, and yet initialized. UPDATE: "sys.scheduler.status.plugin.launched" was the event indicating the Pod creation and is now deprecated. In this version, we still send both ".launched" and ".selected" for the backward compatibility.
• "sys.scheduler.status.plugin.initializing" is newly added to indicate that the Pod of a plugin is being initialized. It could be that initContainer is running or plugin container image is being pulled. Separately, "sys.scheduler.status.plugin.event" may give additional events associated to this state.
• "sys.scheduler.status.plugin.complete" is renamed to "sys.scheduler.status.plugin.completed" Update: this is reverted to support the backward compatibility
• "sys.scheduler.status.plugin.event" is newly added to provide in-depth events of a Pod. This includes containers of a Pod being created, image pulled, and started.

Full description of the events can be found here.