Increase field value max length to 2048 to avoid truncation

of wsrep_provider_options' value. Also increase the max value
length for SYSTEM_VARIABLES schema table.

sql/sql_show.cc

@@ -8619,7 +8619,7 @@ ST_FIELD_INFO variables_fields_info[]=
 {
   {"VARIABLE_NAME", 64, MYSQL_TYPE_STRING, 0, 0, "Variable_name",
    SKIP_OPEN_TABLE},
-  {"VARIABLE_VALUE", 1024, MYSQL_TYPE_STRING, 0, 0, "Value", SKIP_OPEN_TABLE},
+  {"VARIABLE_VALUE", 2048, MYSQL_TYPE_STRING, 0, 0, "Value", SKIP_OPEN_TABLE},
   {0, 0, MYSQL_TYPE_STRING, 0, 0, 0, SKIP_OPEN_TABLE}
 };
 
@@ -8627,10 +8627,10 @@ ST_FIELD_INFO variables_fields_info[]=
 ST_FIELD_INFO sysvars_fields_info[]=
 {
   {"VARIABLE_NAME", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, 0, 0},
-  {"SESSION_VALUE", 1024, MYSQL_TYPE_STRING, 0, MY_I_S_MAYBE_NULL, 0, 0},
-  {"GLOBAL_VALUE", 1024, MYSQL_TYPE_STRING, 0, MY_I_S_MAYBE_NULL, 0, 0},
+  {"SESSION_VALUE", 2048, MYSQL_TYPE_STRING, 0, MY_I_S_MAYBE_NULL, 0, 0},
+  {"GLOBAL_VALUE", 2048, MYSQL_TYPE_STRING, 0, MY_I_S_MAYBE_NULL, 0, 0},
   {"GLOBAL_VALUE_ORIGIN", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, 0, 0},
-  {"DEFAULT_VALUE", 1024, MYSQL_TYPE_STRING, 0, MY_I_S_MAYBE_NULL, 0, 0},
+  {"DEFAULT_VALUE", 2048, MYSQL_TYPE_STRING, 0, MY_I_S_MAYBE_NULL, 0, 0},
   {"VARIABLE_SCOPE", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, 0, 0},
   {"VARIABLE_TYPE", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, 0, 0},
   {"VARIABLE_COMMENT", TABLE_COMMENT_MAXLEN, MYSQL_TYPE_STRING, 0, 0, 0, 0},