Removed single data center restriction for VMware

The single data center restriction no longer applied for the VMware
compute driver as of Havana 2013.2.2. This is an (effective) backport
from master of:

* commit # 1ec1d80051fd8cbb4ed2b1dfb2cc94a3a889d028
* change # I151d4831a74f92c57cd98b96fb0b405d3061b832

Closes-Bug: #1274311
Change-Id: Idec5b2ee9783a91025dc2ac3aa7150bbdda6c990