Fix usage of "|" for tests

With the more recent versions of ansible, we should now use
"is" instead of the "|" sign for the tests.

This should fix it.

Change-Id: Iaab769237a607bf003fb70eb99ade309c112d6ac

tasks/memcached_install.yml

@@ -20,6 +20,6 @@
     update_cache: "{{ (ansible_pkg_mgr == 'apt') | ternary('yes', omit) }}"
     cache_valid_time: "{{ (ansible_pkg_mgr == 'apt') | ternary(cache_timeout, omit) }}"
   register: install_packages
-  until: install_packages | success
+  until: install_packages  is success
   retries: 5
   delay: 2