restapi: API support to query gluster volume profile info

Added an api to return volume profile information

/api/clusters/../glustervolumes/{id}/profilestatistics[;nfsStatistics]

which returns output in format:
<volume_profileDetails>
 <brick_profileDetails>
  <brick_profileDetail>
    <brick><brick_dir>10.70.43.53:/bricks/b2</brick_dir></brick>
    <profile_detail>
      <profile_type>INTERVAL</profile_type>
      <duration>348</duration>
      <statistic id="fa...e"><name>total.bytes.read</name> ...</statistic>
       <block_statistic>
          <statistic id="c2...3"><name>block.size</name> ..</statistic>
          <statistic id="23...7"><name>bytes.read</name> ...</statistic>
          <statistic id="40...2"><name>bytes.write</name> ...</statistic>
       </block_statistic>
       <block_statistic>
       ...
       </block_statistic>
       <fop_statistic>
          <name>LOOKUP</name>
          <statistic id="1d...7"><name>min.latency</name>< ...</statistic>
          ...
       <fop_statistic>
    </profile_detail>
  </brick_profileDetail>
  ...
  <nfs_profileDetails>
     <nfs_profileDetail>
     <nfsServerIp>server-ip</nfsServerIp>
        <profile_detail> ... </profile_detail>
     </nfs_profileDetail>
  </nfs_profileDetails>
</volume_profileDetails>

Change-Id: Iff04cc30f01a7fbe9d6e48b8498d405d05c41c25
Bug-Url: https://bugzilla.redhat.com/1083583
Signed-off-by: Sahina Bose <sabose@redhat.com>