CNI documentation example is not explicit enough about external plugins

I'm testing Mesos 1.0.0-rc1 with Weave CNI. When I switched back to the CNI example stated in the docs and restarted mesos-slave, I received a strange error about not being able to find hadoop.

I think that it's related to this issue: https://issues.apache.org/jira/browse/MESOS-5669

I thought I'd log the issue, but if it has been fixed by the issue above, feel free to close.

The setup, state and logs can be found here: https://gist.github.com/philwinder/8f4c652723fa5c374b86a5e440bf4330