Handle Delete operation if pool not found

If the backend rbd or cephfs pool is already deleted
we need to return success to the  DeleteVolume RPC
call to make it idempotent.

Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>
(cherry picked from commit 8dcb6a6105)

e2e/rbd.go

@@ -325,6 +325,15 @@ var _ = Describe("RBD", func() {
 					Fail(err.Error())
 				}
 			})
+
+			// Make sure this should be last testcase in this file, because
+			// it deletes pool
+			By("Create a PVC and Delete PVC when backend pool deleted", func() {
+				err := pvcDeleteWhenPoolNotFound(pvcPath, false, f)
+				if err != nil {
+					Fail(err.Error())
+				}
+			})
 		})
 	})