extend utils with unixpipe
implement docker cmd and module
add documentation to docker command
syntax and fixes from review
try to avoid spitting errors on "working" failures

Wait a bit for the remote listener to be up before accessing it,
to avoid an ssh channel connection error.

The other fix, considering EADDRINUSE normal and waiting for
the first connection, should rather be implemented as a restart
of the remote process.
Merge pull request #2 from kalou/docker

Implement a minimal docker tunneling ability, via ssh port forwarding. That would be mainly useful for temporary, zeroconf needs.