edx_sandbox.yml: Run edxlocal role only if edxapp db is on localhost

* Makes the mysql role a dependency of edxlocal
* Moves memcached install into new role
* Installs memcached if EDXAPP_MEMCACHE contains localhost

playbooks/edx_sandbox.yml

@@ -34,9 +34,10 @@
       nginx_sites:
       - ecommerce
       when: SANDBOX_ENABLE_ECOMMERCE
-    - role: mysql
+    - role: edxlocal
       when: EDXAPP_MYSQL_HOST == 'localhost'
-    - edxlocal
+    - role: memcache
+      when: "'localhost' in ' '.join(EDXAPP_MEMCACHE)"
     - role: mongo
       when: "'localhost' in EDXAPP_MONGO_HOSTS"
     - { role: 'rabbitmq', rabbitmq_ip: '127.0.0.1' }

playbooks/roles/edxlocal/meta/main.yml

 ---
 dependencies:
   - common
+  - mysql

playbooks/roles/edxlocal/tasks/main.yml

@@ -74,7 +74,3 @@
     name={{ COMMON_MYSQL_ADMIN_USER }}
     password={{ COMMON_MYSQL_ADMIN_PASS }}
     priv='*.*:CREATE USER'
-
-
-- name: install memcached
-  apt: pkg=memcached state=present

playbooks/roles/memcache/tasks/main.yml

+# Installs memcached
+
+- name: install memcached
+  apt: pkg=memcached state=present update_cache=yes
+  tags:
+    - install
+    - install:memcache