We were just emitting Killed/Terminated events before. In v0.8 we
emitted Killing/Killed, but lacked Terminated when explicitly stopping
a task. This change makes it so Terminated is always included, whether
explicitly stopping a task or it exiting on its own.

New output:

2019-01-04T14:58:51-08:00  Killed            Task successfully killed
2019-01-04T14:58:51-08:00  Terminated        Exit Code: 130, Signal: 2
2019-01-04T14:58:51-08:00  Killing           Sent interrupt
2019-01-04T14:58:51-08:00  Leader Task Dead  Leader Task in Group dead
2019-01-04T14:58:49-08:00  Started           Task started by client
2019-01-04T14:58:49-08:00  Task Setup        Building Task Directory
2019-01-04T14:58:49-08:00  Received          Task received by client

Old (v0.8.6) output:

2019-01-04T22:14:54Z  Killed            Task successfully killed
2019-01-04T22:14:54Z  Killing           Sent interrupt. Waiting 5s before force killing
2019-01-04T22:14:54Z  Leader Task Dead  Leader Task in Group dead
2019-01-04T22:14:53Z  Started           Task started by client
2019-01-04T22:14:53Z  Task Setup        Building Task Directory
2019-01-04T22:14:53Z  Received          Task received by client