cli: Fix xml output for volume status

The XML output for volume status was malformed when one of the nodes is
down, leading to outputs like
-------
          <node>
             <node>
               <hostname>NFS Server</hostname>
               <path>localhost</path>
               <peerid>63ca3d2f-8c1f-4b84-b797-b4baddab81fb</peerid>
               <status>1</status>
               <port>2049</port>
               <pid>2130</pid>
             </node>
-----

This was happening because we were starting the <node> element before
determining if node was present, and were not closing it or clearing it
when not finding the node in the dict.

To fix this, the <node> element is only started once a node has been
found in the dict.

Change-Id: I6b6205f14b27a69adb95d85db7b48999aa48d400
BUG: 1046020
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/6571
Reviewed-by: Aravinda VK <avishwan@redhat.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>