Add MYSQL_CONF env var to mariadb, same as mysql, allowing mariadb

plugin users to easily override things. Also, add a commented out 'port'
line in each my.cnf, since this is the most likely change needed.

Author: jefft

plugins/mariadb/my.cnf

@@ -1,6 +1,6 @@
 # MySQL configuration file
 
 [mariadbd]
-# Change this port if 3360 is already used
-#port = 3360
+# Change this port if 3306 is already used
+#port = 3306
 log_error=mysql.log

plugins/mysql/my.cnf

@@ -2,5 +2,5 @@
 
 # [mysqld]
 # skip-log-bin
-# Change this port if 3360 is already used
-#port = 3360
+# Change this port if 3306 is already used
+#port = 3306