switch memcached from tcp to unix domain socket

installer/roles/local_docker/tasks/compose.yml

@@ -10,6 +10,12 @@
     state: directory
     mode: 0777
 
+- name: Create Memcached socket directory
+  file:
+    path: "{{ docker_compose_dir }}/memcached_socket"
+    state: directory
+    mode: 0777
+
 - name: Create Docker Compose Configuration
   template:
     src: "{{ item }}.j2"