`howl`: fill in `command_id` of run stop

[rerpha]

the command_id of a run stop is actually a required field but we just set it to None - we should instead use a uuid like we do for the job id, though i dont think the run stop command_id actually needs to be passed through so it can just be a new uuid created at the time of setting the args for a run stop.

[rerpha]

@danielmaclaren fancy having a go at this one too?

[rerpha]

this is sort of related to ISISComputingGroup/streaming-data-types#11 in that the schema itself should have required fields set, we should still do this ticket so that we're ready for when we change the schema.