Document headless VirtualBox and Vagrant config to disable MAC filtering
Merge pull request #46 from dineshs-altiscale/vagrant

Document headless VirtualBox and Vagrant config to disable MAC filtering
Update to work with libcontainer

Makes pipework work with the new docker native exec driver (libcontainer).
Use pid from docker inpsect

Since docker returns a pid for the container use that instead of doing all the other hackery.
Merge pull request #41 from cpuguy83/patch-2

Update to work with libcontainer