Apply deployment env vars during keystone main_pre

This will be required for tasks that need external http
access, such as package installations as part of main_pre
tasks file.

Change-Id: I285f34f2b657f1d7e6436505bd39e025e504bfa9

playbooks/os-keystone-install.yml

@@ -43,6 +43,7 @@
 - name: Pre-service deployment
   hosts: keystone_all
   gather_facts: false
+  environment: "{{ deployment_environment_variables | default({}) }}"
   tasks:
     - name: "Pre-service deployment tasks from os_keystone role"
       include_role: