Pass fatal-failure reasons to the target logs
Pass fatal-failure reasons to the target logs

This is related to #169 which was difficult to debug because I had forgot to
include fill the `?log` arguments in the `Target.Automaton.transition` function;
now we get:

    * [n]: Some Name
    ketrew_2015-04-27-23h33m29s668ms-UTC_333944412
    Failed_to_start {2015-04-27-23h34m51s717ms-UTC (Host: Cmd
      "python '/.../ketrew-playground/ketrew_2015-04-27-23h34m50s769ms-UTC_671426885/daemonizator.py'"
      returned 1)}

hammerlab/ketrew