rbd: provide host-path for rbd-nbd logging

Problem:
--------
1. rbd-nbd by default logs to /var/log/ceph/ceph-client.admin.log,
Unfortunately, container doesn't have /var/log/ceph directory hence
rbd-nbd is not logging now.
2. Rbd-nbd logs are not persistent across nodeplugin restarts.

Solution:
--------
Provide a host path so that log directory is made available, and the
logs persist on the hostnode across container restarts.

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>

deploy/rbd/kubernetes/csi-rbdplugin.yaml

@@ -111,6 +111,8 @@ spec:
               mountPropagation: "Bidirectional"
             - name: keys-tmp-dir
               mountPath: /tmp/csi/keys
+            - name: ceph-logdir
+              mountPath: /var/log/ceph
         - name: liveness-prometheus
           securityContext:
             privileged: true
@@ -146,6 +148,10 @@ spec:
           hostPath:
             path: /var/lib/kubelet/pods
             type: DirectoryOrCreate
+        - name: ceph-logdir
+          hostPath:
+            path: /var/log/ceph
+            type: DirectoryOrCreate
         - name: registration-dir
           hostPath:
             path: /var/lib/kubelet/plugins_registry/