Make windows server 2012 default for SQL 2014 (#321)

sql-2014-standalone/azuredeploy.json

@@ -51,7 +51,7 @@
         },
         "windowsOSVersion": {
             "type": "string",
-            "defaultValue": "2016-Datacenter",
+            "defaultValue": "2012-R2-Datacenter",
             "allowedValues": [
                 "2016-Datacenter",
                 "2012-R2-Datacenter"