Ensure packages for octavia only when EnablePackageInstall is True

Changing the ansible task for ensuring packages to run only when
EnablePackageInstall is True.
Also removed the step4 tag from this task as there are no tags
in host_prep_tasks.

Change-Id: I1374b20ec66694fe661183e089f8d88473be11a9

docker/services/octavia-worker.yaml

@@ -36,6 +36,10 @@ parameters:
     default: {}
     description: Parameters specific to the role
     type: json
+  EnablePackageInstall:
+    default: 'false'
+    description: Set to true to enable package installation at deploy time
+    type: boolean
 
 resources:
 
@@ -134,11 +138,11 @@ outputs:
           ignore_errors: true
         - name: Ensure packages required for configuring octavia are present
           yum: name={{item}}  state=present
-          tags: step4
           with_items:
             - python2-neutronclient
             - python2-openstackclient
             - openssl
+          when: {get_param: EnablePackageInstall}
       upgrade_tasks:
         - name: Stop and disable octavia_worker service
           when: step|int == 2