Fix baremetal stats type

As of 8a7b95dccdbe449d5235868781b30edebd34bacd the resource
tracker code is expecting stats to be a json string.  Baremetal
was setting it to a dict and it was breaking the db write.

Change-Id: I708fecd623c1a42d002c2b20bfdf06b625c9c287
Closes-Bug: #1279572
Merge "Fix baremetal stats type"