ProxyCommand support

[igorwwwwwwwwwwwwwwwwwwww]

This is a feature request.

I was trying to use katyusha, but was not able to get it working due to missing ProxyCommand support. We are relying on ProxyCommand to proxy through a bastion host.

The result was something along these lines:

$ katyusha run 'api-*' env=prod -- hostname

20000 done, 0 ok, 0 fail, 20000 error in 0s
hostname
api-01.prod.internal      dial tcp: lookup api-01.prod.internal: no such host after 0s
api-02.prod.internal      dial tcp: lookup api-02.prod.internal: no such host after 0s
...

Using roughly this kind of ssh config:

Host *.prod.internal
  ProxyCommand bash -c "ssh bastion.prod.example.com -W %h:%p"

The bastion host is used not only to proxy the connection, but also for DNS resolution of the target hostname.