Fixes host stats for VMWareVCDriver

Host stats for VCDriver should collect aggregate cluster stats
rather than that of a single host in the cluster.

Fixes: bug #1190515

(cherry picked from commit fddcde6a063d59596f687f0651af94f498f7d9b7)

Change-Id: I56b6b027e1370fc2cfdb4d87c10b80574a81b225