Check the output of the cmd.run_all function call.

def _check_cmd(call):
    '''
    Check the output of the cmd.run_all function call.
    '''
    if call['retcode'] != 0:
        comment = ''
        std_err = call.get('stderr')
        std_out = call.get('stdout')
        if std_err:
            comment += std_err
        if std_out:
            comment += std_out

        raise CommandExecutionError('Error running command: {0}'.format(comment))

    return call