cfn template: commands hostnames within VPC

It's a bummer that enabling VPC DNS hostnames isn't supported by
CloudFormation yet, so we have to do this manual command hack like
we're already doing for ElastiCache. Helpful bit for configuring your
ssh as well.

cloudformation_templates/edx-reference-architecture.json

@@ -3200,6 +3200,49 @@
           ]
         ]
       }
+    },
+    "EnableDNSHostnamesForVPCCommand":{
+      "Description":"MANUAL COMMAND #3: Change VPC setting to enable automatic DNS hostname resolution from within the VPC. Setting not supported in Cloudformation yet.",
+      "Value":{
+        "Fn::Join":[
+          "",
+          [
+            "ec2-modify-vpc-attribute ",
+            "-c ", { "Ref":"EdxVPC" }, " ",
+            "-d true"
+          ]
+        ]
+      }
+    },
+    "SSHConfigStanza":{
+      "Description":"This is the configuration bits you will need to add to your personal ssh config file to use the bastion host to access machines in your VPC. Typically ~/.ssh/config.",
+      "Value":{
+        "Fn::Join":[
+          "\n",
+          [
+            {
+              "Fn::Join":[
+                "",
+                [
+                  "Host *.", { "Ref":"AWS::Region" },
+                  "-c ", { "Ref":"EdxVPC" }, " ",
+                  "-d true"
+                ]
+              ]
+            },
+            {
+              "Fn::Join":[
+                "",
+                [
+                  "  ProxyCommand ssh -W %h:%p ", { "Ref":"BastionIPAddress" }
+                ]
+              ]
+            },
+            "  ForwardAgent yes ",
+            "  User ubuntu"
+          ]
+        ]
+      }
     }
   }
 }