Signed SSH Certificates Support

[freddierice]

I have a use-case where I need to use Signed SSH Certificates to log into remote servers to run remote-shell-cmd and remote-shell-script runners. The underlying paramiko library supports this by running the load_certificate function on a dedicated PKey.

I'd like to propose adding a runner_parameter certificate to the BaseParallelSSHRunner that can optionally be leveraged by the underlying *SSHClients to log into remote servers.

If the certificate is not present, just do the same as before. If the parameter exists, load it to the paramiko.pkey.PKey so that it can be used for the SSH connection.

Extra reading:

• Example creating signed ssh keys
• load_certificate