cli,glusterd: Task parameters in xml output

This patch introduces task parameters for the asynchronus task shown in
volume status. The parameters are only given for xml output. The
parameters shown currently are,
- source and destination bricks for replace-brick tasks
  ......
        <tasks>
          <task>
            <type>Replace brick</type>
            <id>3d1a1005-9d2e-4ae0-bd62-577bc1d333a3</id>
            <status>1</status>
            <params>
              <srcBrick>archm:/export/test4</srcBrick>
              <dstBrick>archm:/export/test-replace1</dstBrick>
            </params>
          </task>
        </tasks>
  ......
- list of bricks being removed for remove-brick tasks
  ......
        <tasks>
          <task>
            <type>Remove brick</type>
            <id>901c20ca-0da2-41de-8669-5f0caca6b846</id>
            <status>1</status>
            <params>
              <brick>archm:/export/test2</brick>
              <brick>archm:/export/test3</brick>
            </params>
          </task>
        </tasks>
  ......

The changes for non-xml output will be done in a subsequent patch.

Change-Id: I322afe2f83ed8adeddb99f7962c25911204dc204
BUG: 916577
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/5771
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Vijay Bellur <vbellur@redhat.com>