Add the list of hw_version supported by vmware driver.

This patch add the list of hw_version supported by vmware driver.
The corresponding relationships are as following:
vmx-13: ESXi6.5
vmx-11: ESXi6.0
vmx-10: ESXi5.5
vmx-09: ESXi5.1
vmx-08: ESXi5.0
vmx-07: ESXi/ESX4.x
vmx-04: ESX3.x
vmx-03: ESX2.x

Change-Id: I1796b461855081f758b0585c9a0165c5138669d5

etc/metadefs/compute-vmware-flavor.json

@@ -13,7 +13,17 @@
         "vmware:hw_version": {
             "title": "VMware Hardware Version",
             "description": "Specifies the hardware version VMware uses to create images. If the hardware version needs to be compatible with a cluster version, for backward compatibility or other circumstances, the vmware:hw_version key specifies a virtual machine hardware version. In the event that a cluster has mixed host version types, the key will enable the vCenter to place the cluster on the correct host.",
-            "type": "string"
+            "type": "string",
+            "enum": [
+                "vmx-13",
+                "vmx-11",
+                "vmx-10",
+                "vmx-09",
+                "vmx-08",
+                "vmx-07",
+                "vmx-04",
+                "vmx-03"
+            ]
         },
         "vmware:storage_policy": {
             "title": "VMware Storage Policy",