Behavior for pyghmi.console.Console(iohandler) doesn't match doc

[Katrina]

According to [docstring](https://github.com/openstack/pyghmi/blob/master/pyghmi/ipmi/console.py#L36-L38) the `iohandler` arg in pyghmi.console.Console can be "Either a function to call with bytes, a filehandle to use for input and output, or a tuple of (input, output) handles". However, if a tuple is provided, as soon as there is something to output, it throws error:

```
  File "/path/to/repo/pyghmi/pyghmi/ipmi/console.py", line 301, in _print_data
    self.out_handler(data)
TypeError: 'tuple' object is not callable
```

Seems like pyghmi is now expecting a callable function and does not accept a tuple of handles:
https://github.com/openstack/pyghmi/blob/master/pyghmi/ipmi/console.py#L301

Looks like change in behavior was introduced here:
https://github.com/openstack/pyghmi/commit/e9000313f2cef935edd3eb9a9c57128995b5c0be