cli,glusterd: Task parameters in xml output

 Backport of 91cd0eae2cc1d96cbafa6457835f146503355238 from master

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.

BUG: 916577
Change-Id: Iade8a4974aefc5ffb080553496ae5a3169055090
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/5973
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>