Fix leaving system table as InnoDB engine

Fix the test case main.servers to restore the table mysql.servers back to Aria
engine, not leave it changed to InnoDB. This was causing the test case
innodb.innodb_stats to fail sporadically if it was run after main.servers.

Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

Author: knielsen

mysql-test/main/servers.result

@@ -50,3 +50,4 @@ CREATE SERVER s1 FOREIGN DATA WRAPPER mysql OPTIONS (HOST '127.0.0.1');
 ALTER TABLE mysql.servers ENGINE=innodb;
 FLUSH PRIVILEGES;
 drop server s1;
+ALTER TABLE mysql.servers ENGINE=Aria;

mysql-test/main/servers.test

@@ -50,3 +50,5 @@ CREATE SERVER s1 FOREIGN DATA WRAPPER mysql OPTIONS (HOST '127.0.0.1');
 ALTER TABLE mysql.servers ENGINE=innodb;
 FLUSH PRIVILEGES;
 drop server s1;
+# Restore the table back to original engine, to not disrupt following tests.
+ALTER TABLE mysql.servers ENGINE=Aria;