Scripts added to deregister admin app from ELB on deploy

- Application Stop state will deregister
- Application Start state re-registers

Ensures that the App instance is not receiving traffic before stopping the app as part of a code deploy

These scripts are from :

https://blogs.aws.amazon.com/application-management/post/Tx39X8HM93NXU47/Use-AWS-CodeDeploy-to-Deploy-to-Amazon-EC2-Instances-Behind-an-Elastic-Load-Bala

Adapted to remove notion of Autoscaling groups (which we don't use) and to use a named ELB, allows common file to be common and start/stop to be changed.

appspec.yml

@@ -14,14 +14,24 @@ hooks:
       runas: root
       timeout: 300
   ApplicationStart:
-    - 
+    -
       location: scripts/aws_start_app.sh
       runas: root
       timeout: 300
-  ApplicationStop: 
+    -
+      location: scripts/register_with_elb.sh
+      runas: root
+      timeout: 300
+  ApplicationStop:
+    -
+      location: scripts/deregister_from_elb.sh
+      runas: root
+      timeout: 300
     - 
       location: scripts/aws_stop_app.sh
       runas: root
       timeout: 300
 os: linux
 version: 0.0
+
+