Make ssh_config paramiko 1.12/1.13 compatible

`ssh_config.py` tries to make a hash of hostnames like this:

    ret_dict[d['host']] = _copy

This fails, because d['host'] is a list, which you cannot hash. It's been a list since at least 2012 in the Paramiko codebase.

This also searches the `_copy` dictionary for various keys- user, hostname, etc. This is not going to work with Paramiko 1.12/1.13, where those keys are actually inside another dictionary, kept inside of the 'config' key.