Adding a sleep time for the container to start its processes

For https://github.com/jenkinsci/docker-plugin/issues/36

The first thing I tried to do was redo the connect step (https://github.com/jenkinsci/docker-plugin/blob/master/src/main/java/com/nirima/jenkins/plugins/docker/DockerCloud.java#L167) if it failed to connect, however this was creating more problems (and should probably be at the SlaveComputer level?) and even then wasn't connecting.  If someone else has an idea of where to retry connecting to the slave then I'll be more than happy to look into that though.