tree 4e3a45cfeede1e54cdee4134c88f2235f37fbe55
parent 2d6108bb4bf5f875d229b8d3fdfa7040505ed5e0
author Jordan Ly <jordan.ly8@gmail.com> 1523482912 -0700
committer Jordan Ly <jly@twitter.com> 1523482912 -0700

Add more preemption metrics (jobs preempted, preemptors) and logging statements

Added additional metrics: ```
1. preemptor_tasks_preempted_[JOB_NAME] - The number of times [JOB_NAME] has
   been preempted for another task.
2. preemptor_tasks_preemptor_[JOB_NAME] - The number of times [JOB_NAME] has
   preempted another task.
3. preemptor_slot_search_[success|failed]_for_[JOB_NAME] - The number of times
   [JOB_NAME] has or hasn't found a slot for preemption.
4. preemptor_slot_validation_[success|failed]_for_[JOB_NAME] - The number of
   times [JOB_NAME] succeeded to or failed to validate a slot before
preemption.  ```

Additionally, added some `LOG.info` statements for better visibility into
preemption/preemption slot finding.

Did a little bit of code refactoring as well.

Reviewed at https://reviews.apache.org/r/66536/