Remove dependency on 'ssh' command for proxying

[pkittenis]

Currently proxy support is done through paramiko which uses ProxyCommand as read from ~/.ssh/config and runs the proxy command in a shell.

Normally the proxy command is another ssh command to a bastion host, which means proxying needs

• openssh installed
• shell command per host connection to do the proxying, meaning a shell process for each host. This is inefficient and can lead to high system load for large host lists

As an enhancement change proxying so that:

• done in native python, no external utilities or shell comands used
• add a proxy module to fake_server
• add tests using the above