disable start_io_logging_thread if :logger is set to a Logger.new(STDOUT)
disable start_io_logging_thread if :logger is set to a Logger.new(STDOUT)

If :logger option is set unexpectedly, reading from STDOUT/ERR and
writing to :logger could cause infinite loop because
:logger may write data to STDOUT/ERR.

In this case, try_get_io_from_logger is unnecessary, and harmful.
Possibly fixes #21.

naritta/serverengine,fluent/serverengine