Issue LIBCLOUD-499: Add support for ssh_config and proxycommand

since 1.10 paramiko supports ssh_config parsing and proxycommand.

Proxycommand is essential if you have a ssh gateway between you and your computes. Some big infrastructures does.
Seems like copy and paste error. Should be `conninfo['port']`, right?

Ideally, we would also have a test case for every if branch.