Several small fixes to alton automation

Add usage example to alton playbook
Allow alton to use most recent redis version
HEAD is a local-specific value. Instead, we should check out master.

playbooks/edx-east/alton.yml

 # Configure an admin instance with jenkins and asgard.
+# Usage: ansible-playbook alton.yml -i <admin-host>, -e <secure-repo>/admin/edx_admin.yml -e <secure-repo>/admin/admin.yml
 - name: Configure instance(s)
   hosts: all
   sudo: True

playbooks/roles/alton/defaults/main.yml

@@ -54,7 +54,7 @@ alton_venv_dir: "{{ alton_venvs_dir }}/alton"
 alton_venv_bin: "{{ alton_venv_dir }}/bin"
 
 alton_source_repo: "https://github.com/edx/alton.git"
-alton_version: "HEAD"
+alton_version: "master"
 alton_requirements_file: "{{ alton_code_dir }}/requirements.txt"
 
 alton_supervisor_wrapper: "{{ alton_app_dir }}/alton-supervisor.sh"

playbooks/roles/alton/meta/main.yml

@@ -22,4 +22,6 @@
 dependencies:
   - common
   - supervisor
-  - redis
+  - role: redis
+    redis_debian_pkgs:
+      - "redis-server"