fix(mariadb): encode Popen() returns

subprocess.Popen() returns byte object by defect which has issue with
operations that treats thing as str. This ensure Popen() encodes the
return as utf-8 before we do anything.

Change-Id: I321771f69cfcb492be1308c61313a0598b1e766a
Signed-off-by: Tin Lam <tin@irrational.io>

mariadb/templates/bin/_start.py.tpl

@@ -547,7 +547,8 @@ def update_grastate_on_restart():
                         '--wsrep_cluster_address=gcomm://', '--wsrep-recover'
                     ],
                     stdout=subprocess.PIPE,
-                    stderr=subprocess.PIPE)
+                    stderr=subprocess.PIPE,
+                    encoding="utf-8")
                 out, err = wsrep_recover.communicate()
                 wsrep_rec_pos = '-1'
                 for item in err.split("\n"):