Filtering server products based on the region context.
Setting VM IP addresses.
Allow for null snapshot source disks

Google SDK docs say:
"The source disk used to create this snapshot. Once the source disk
 has been deleted from the system, this field will be cleared, and
will not be set even if a disk with the same name has been re-created."
Check for null source image in toVirtualMachine()
Only return data centers in the requested region

Copied the cache handling strategy from AWS driver
Fix Firewall providerVlanId
Merge pull request #29 from labisso/rollup-pr

Rollup PR against develop