Automatic merge from submit-queue

StorageOS Volume Plugin

**What this PR does / why we need it**:
This PR adds a new volume plugin for StorageOS volumes.  StorageOS runs as a container on Kubelet nodes, aggregating local or attached storage and making its capacity available to all nodes within the cluster. More information at http://storageos.com.

The StorageOS plugin supports:

1. Dynamic Provisioning using Storage Classes
2. Persistent Volumes and Persistent Volume Claims.

**Which issue this PR fixes**
A feature request has been created:
https://github.com/kubernetes/features/issues/190

This isn't on the schedule for 1.6 as I wasn't sure when it would be ready.  We intend to make the StorageOS container openly available within the 1.6 lifetime.

**Special notes for your reviewer**:

Separate commits for feature and godep changes.

**Release note**:
```release-note
StorageOS Volume Driver
[StorageOS](http://www.storageos.com) can be used as a storage provider for Kubernetes.  With StorageOS, capacity from local or attached storage is pooled across the cluster, providing converged infrastructure for cloud-native applications. 
```