Fixes issues found in /os-hosts API

There are some issues found in Cinder /os-hosts API:

1) Bracket in the wrong spot in Cinder HostController show method
There is an erroneous bracket on the following line in the show method
that should be at the end of the response:
   'total_volume_gb': str(sum)},

2) XML Attributes Missing for List/Index method in Cinder HostController
The HostIndexTemplate class specifies mapping for "host" and "topic"
attributes rather than any of the ones that are actually returned from
the index method.

3) XML Serialization is commented for Cinder HostController show method

Fixes Bug: 1139984

Change-Id: I881e80b5e109ed6ddcc4f7c4bf5749ab6dca563d
Merge "Fixes issues found in /os-hosts API"