fix #1701 - MySQL 5.7 defaults break database character set check

extensions/mysql-metadata-storage/src/main/java/io/druid/metadata/storage/mysql/MySQLConnector.java

@@ -30,6 +30,7 @@ import org.apache.commons.dbcp2.BasicDataSource;
 import org.skife.jdbi.v2.DBI;
 import org.skife.jdbi.v2.Handle;
 import org.skife.jdbi.v2.tweak.HandleCallback;
+import org.skife.jdbi.v2.util.BooleanMapper;
 
 import java.sql.SQLException;
 
@@ -77,16 +78,14 @@ public class MySQLConnector extends SQLMetadataConnector
   {
     // ensure database defaults to utf8, otherwise bail
     boolean isUtf8 = handle
-                         .createQuery("SHOW VARIABLES where variable_name = 'character_set_database' and value = 'utf8'")
-                         .list()
-                         .size() == 1;
+                         .createQuery("SELECT @@character_set_database = 'utf8'")
+                         .map(BooleanMapper.FIRST)
+                         .first();
 
     if (!isUtf8) {
       throw new ISE(
           "Database default character set is not UTF-8." + System.lineSeparator()
           + "  Druid requires its MySQL database to be created using UTF-8 as default character set."
-          + " If you are upgrading from Druid 0.6.x, please make all tables have been converted to utf8 and change the database default."
-          + " For more information on how to convert and set the default, please refer to section on updating from 0.6.x in the Druid 0.7.1 release notes."
       );
     }