Implement STAGE_UNSTAGE_VOLUME capability

Summary: Before this, we directly mounted the the rawfile on the mountpoint. In this revision the `STAGE_UNSTAGE_VOLUME` capability is implemented, meaning that the volume is first mounted to a staging path, and then `bind`-mounted to the actual path. This way we can free up loopback devices when they are not needed.

Test Plan:
- Create a pvc, and use it inside a pod
- Run `losetup -l` on the node running the pod, and assert the creation of a loop device
- Delete the pod, but not the pvc
- Run `losetup -l` on the same node, and assert the removal of the loop device

Reviewers: h.marvi, bghadiri

Differential Revision: https://phab.hamravesh.ir/D806

deploy/charts/rawfile-csi/Chart.yaml

@@ -2,5 +2,5 @@ apiVersion: v2
 name: rawfile-csi
 description: RawFile Driver Container Storage Interface
 type: application
-version: 0.1.2
+version: 0.1.3
 appVersion: 0.0.1

deploy/charts/rawfile-csi/templates/01-node-plugin.yaml

@@ -47,7 +47,7 @@ spec:
             type: DirectoryOrCreate
         - name: mountpoint-dir
           hostPath:
-            path: /var/lib/kubelet/pods
+            path: /var/lib/kubelet
             type: DirectoryOrCreate
         - name: data-dir
           hostPath:
@@ -76,7 +76,7 @@ spec:
             - name: socket-dir
               mountPath: /csi
             - name: mountpoint-dir
-              mountPath: /var/lib/kubelet/pods
+              mountPath: /var/lib/kubelet
               mountPropagation: "Bidirectional"
             - name: data-dir
               mountPath: /data