Use more reliable way to get mysql version

mysqladmin --version displays version of client instead of server one.
So we should make decision to run mysql upgrade or not based
on the server version. Also this task should be ran only when mariadb
is already deployed.
This will make possible to be more independent from client version.

Change-Id: Icd20b8c81337d37fba219aa6be482b391bdaedde

tasks/galera_upgrade.yml

@@ -17,8 +17,8 @@
 #                  version. If it is not assume it's nothing is installed.
 - name: Check mysql version
   shell: >
-    if which mysqladmin; then
-      mysqladmin --version | grep -w "{{ galera_major_version }}"
+    if which mysql; then
+      mysql -e "SHOW VARIABLES LIKE 'version';" --batch --skip-column-names | grep -w "{{ galera_major_version }}"
     fi
   register: mysqladmin_version
   changed_when: false

tasks/main.yml

@@ -83,6 +83,7 @@
     - always
 
 - include_tasks: galera_upgrade.yml
+  when: galera_deployed | bool
   tags:
     - galera_server-upgrade