Remove "warn" parameter from command module

This is removed in ansible 2.14.

Change-Id: If48e13dc22d5fbe004444ba9ba74999512ff22c5

tasks/galera_install_dnf.yml

@@ -33,7 +33,6 @@
   changed_when: _remove_existing_mariadb_packages.rc == 2
   failed_when: _remove_existing_mariadb_packages.rc not in [0, 2]
   args:
-    warn: no
     executable: /bin/bash
 
 # In CentOS systems, /etc/my.cnf.d may already exist on the
@@ -133,8 +132,6 @@
 # cleaned out whenever the repo config changes.
 - name: Force the expiry of the repo metadata
   command: "{{ ansible_facts['pkg_mgr'] }} clean metadata"
-  args:
-    warn: no
   when: add_galera_repos is changed
   tags:
     - skip_ansible_lint

tasks/galera_server_upgrade_pre.yml

@@ -18,11 +18,9 @@
 # cause the service stop task to fail. To cater for this
 # we only try to stop the service is it exists.
 - name: Check whether a mysql service exists yet
-  shell: >-
-    systemctl list-unit-files --state=enabled --type=service | grep "^{{ galera_mariadb_service_name }}.service .* enabled$"
+  shell: systemctl list-unit-files --state=enabled --type=service | grep "^{{ galera_mariadb_service_name }}.service .* enabled$" # noqa command-instead-of-module risky-shell-pipe
   args:
     executable: /bin/bash
-    warn: no
   changed_when: false
   failed_when: false
   register: _mysql_service_exists