Portworx Volume Driver in Kubernetes

- Add a new type PortworxVolumeSource
- Implement the kubernetes volume plugin for Portworx Volumes under pkg/volume/portworx
- The Portworx Volume Driver uses the libopenstorage/openstorage specifications and apis for volume operations.

Changes for k8s configuration and examples for portworx volumes.

- Add PortworxVolume hooks in kubectl, kube-controller-manager and validation.
- Add a README for PortworxVolume usage as PVs, PVCs and StorageClass.
- Add example spec files

Handle code review comments.

- Modified READMEs to incorporate to suggestions.
- Add a test for ReadWriteMany access mode.
- Use util.UnmountPath in TearDown.
- Add ReadOnly flag to PortworxVolumeSource
- Use hostname:port instead of unix sockets
- Delete the mount dir in TearDown.
- Fix link issue in persistentvolumes README
- In unit test check for mountpath after Setup is done.
- Add PVC Claim Name as a Portworx Volume Label

Generated code and documentation.
- Updated swagger spec
- Updated api-reference docs
- Updated generated code under pkg/api/v1

Godeps update for Portworx Volume Driver
- Adds github.com/libopenstorage/openstorage
- Adds go.pedge.io/pb/go/google/protobuf
- Updates Godep Licenses

examples/persistent-volume-provisioning/README.md

@@ -63,6 +63,30 @@ parameters:
 
 * `diskformat`: `thin`, `zeroedthick` and `eagerzeroedthick`. See vSphere docs for details. Default: `"thin"`.
 
+#### Portworx Volume
+
+```yaml
+kind: StorageClass
+apiVersion: storage.k8s.io/v1beta1
+metadata:
+  name: portworx-io-priority-high
+provisioner: kubernetes.io/portworx-volume
+parameters:
+  repl: "1"
+  snap_interval:   "70"
+  io_priority:  "high"
+
+```
+
+*  `fs`: filesystem to be laid out: [none/xfs/ext4] (default: `ext4`)
+*  `block_size`: block size in Kbytes (default: `32`)
+*  `repl`: replication factor [1..3] (default: `1`)
+*  `io_priority`: IO Priority: [high/medium/low] (default: `low`)
+*  `snap_interval`: snapshot interval in minutes, 0 disables snaps (default: `0`)
+*  `aggregation_level`: specifies the number of chunks the volume would be distributed into, 0 indicates a non-aggregated volume (default: `0`)
+*  `ephemeral`: ephemeral storage [true/false] (default `false`)
+
+For a complete example refer ([Portworx Volume docs](../../volumes/portworx/README.md))
 
 #### GLUSTERFS