MXS-2813: Mask password values in output

The password values are now masked with asterisks. This tells whether a
password is set or not but it does not expose any information about the
password itself.

include/maxscale/modinfo.h

@@ -80,6 +80,7 @@ enum mxs_module_param_type
     MXS_MODULE_PARAM_BOOL,          /**< Boolean value */
     MXS_MODULE_PARAM_STRING,        /**< String value */
     MXS_MODULE_PARAM_QUOTEDSTRING,  /**< String enclosed in '"':s */
+    MXS_MODULE_PARAM_PASSWORD,      /**< Password value that is masked in all output  */
     MXS_MODULE_PARAM_ENUM,          /**< Enumeration of string values */
     MXS_MODULE_PARAM_PATH,          /**< Path to a file or a directory */
     MXS_MODULE_PARAM_SERVICE,       /**< Service name */
@@ -245,6 +246,9 @@ static inline const char* mxs_module_param_type_to_string(enum mxs_module_param_
     case MXS_MODULE_PARAM_STRING:
         return "string";
 
+    case MXS_MODULE_PARAM_PASSWORD:
+        return "password string";
+
     case MXS_MODULE_PARAM_QUOTEDSTRING:
         return "quoted string";