'Looks up for koji or brew "binaries" on the system
Systems with plain koji usually don\'t have a brew cmd, while systems
with koji, have *both* koji and brew utilities. So we look for brew
first, and if found, we consider that the system is configured for
brew. If not, we consider this is a system with plain koji.
:return: either koji or brew command line executable path, or None'

def get_default_command(self):

    koji_command = None
    for command in self.CMD_LOOKUP_ORDER:
        if os.path.isfile(command):
            koji_command = command
            break
        else:
            koji_command_basename = os.path.basename(command)
            try:
                koji_command = os_dep.command(koji_command_basename)
                break
            except ValueError:
                pass
    return koji_command
