NFS: Support subfolder jailing without docker volume create for Clusters

[gondor]

This is an addon and experimental feature to extend Issue #72.

Within clusters like Mesos we don't have the ability to use a common NFS mount and create subfolders during mount time to root the container in. This is due to the fact that Issue #72 requires us using docker volume create -d nfs --name data1 -o share=nfshost:/export -o create=true before the container is started.

Since Docker doesn't support share-opts when using docker run we are using a delimiter in this feature to support this.

For example this allows us to use a common nfs share - say nfshost:/export and create a subfolder for the new container within /export called data1. The ultimate mount would be /export/data1.

Syntax now supported:

docker run --volume-driver=nfs -v nfshost/export#data1:/data nginx

The # delimiter seperate the share and the vol name.