Update dockerpty to fix discovered race condition.

Signed-off-by: Chris Corbyn <chris@w3style.co.uk>
Merge pull request #272 from d11wtq/bugfix/race_condition

Update dockerpty to fix discovered race condition.
Update dockerpty; stub it out in tests

Its current behaviour occasionally causes tests to hang; until this is
resolved, we'll stub it out. We weren't testing the output of 'run'
anyhow (though we should be).
Support for host address in port bindings (Closes #267)