SSH bug fix

SSH bug fix
Changing line 28 to `default_connect_kwargs = {'hostname': None'}` might work, or doing something similar to the handling of `timeout`, `allow_agent`, etc.

That all said, given the original Exception of `AttributeError: 'SSHClient' object has no attribute '_connect_kwargs'`, I think your original plan of moving the `set_missing_host_key_policy` down below where `self._connect_kwargs` is set should have no effect on how this class works, aside from helping prevent `__repr__` from exploding.