If an unknown command or a phase is called consistently
return the same error.
If a command that has subcommands is called
return an error.
To achieve the above add a new util function
RequireSubcommand() that sets NoArgs and RunE for
regular commands or a "phase" command.
Remove MacroCommandLongDescription and just return an
error that a subcommand is required from the phase runner.
Fix minor comments capitalization.
Perform other minor fixes in util/error.go.
b497d28d43