rbd: add generic ephemeral volume validation

This commit adds the validation of csi RBD driver to work with
ephemeral volume support. With ephemeral volume support a user can
specify ephemeral volumes in its pod spec and tie the lifecycle
of the PVC with the POD.

An example pod spec is also included in this commit.

Signed-off-by: Humble Chirammal <hchiramm@redhat.com>

examples/rbd/pod-ephemeral.yaml

@@ -0,0 +1,23 @@
+---
+apiVersion: v1
+kind: Pod
+metadata:
+  name: csi-rbd-demo-ephemeral-pod
+spec:
+  containers:
+    - name: web-server
+      image: docker.io/library/nginx:latest
+      volumeMounts:
+        - mountPath: /myspace
+          name: mypvc
+  volumes:
+    - name: mypvc
+      ephemeral:
+        volumeClaimTemplate:
+          spec:
+            accessModes:
+              - ReadWriteOnce
+            storageClassName: csi-rbd-sc
+            resources:
+              requests:
+                storage: 1Gi