Several `nomad job` subcommands had duplicate or slightly similar logic
for resolving a job ID from a CLI argument prefix, while others did not
have this functionality at all.
This commit pulls the shared logic to the command Meta and updates all
`nomad job` subcommands to use it.
The only user of monitor(evalID, true) was command/eval_status, and
eval_status had a duplicate of the prefix-handling code inside it, so in
all cases the complete evalID was being passed to monitor.
Given that, we can remove the prefix code from command/monitor, and
remove the boolean arg.
