Closes-Bug: #1378454
  Issue: Add sensor_type to ipmi.sandesh so that sorting/querying data
         becomes easier. Break the fied 'reading' into 'unit' and 'reading'
  Fix: Made the above changes
  Test: Tested it on server-manager node

  Made changes based on review-1
Change-Id: Ida0f9018f6055a3b7ee0bcfcb50563b98aaef886