AURORA-78: automate and enforce release workflow

Adds scripts to generate the CHANGELOG from JIRA, create the
release candidate, generate the release candidate VOTE email draft,
generate the release from the release candidate and the RESULT VOTE
email draft. docs/committers.md added with process flow details.

Testing Done:
Have been running these in dry-run mode, getting to the point where I can not test the release script as it requires things to be published to the dev dist. Have some changes in release script that are pending, but wanted to get feedback on the release-candidate and docs.

Bugs closed: AURORA-78

Reviewed at https://reviews.apache.org/r/19710/
Dropping "No jobs to kill" error from killTasks.

Bugs closed: AURORA-345

Reviewed at https://reviews.apache.org/r/20732/