Move the InnoDB Plugin tests from storage/innodb_plugin/mysql-test/ where

they are ignored to a new test suite "innodb_plugin".

Remove a hack in mtr that was deployed to run the builtin InnoDB tests against
the InnoDB Plugin. Also detect if a test is an 'innodb plugin test' and if so
then transparently replace the builtin InnoDB with the InnoDB Plugin.

mysql-test/suite/innodb_plugin/t/innodb_bug51920.test

@@ -0,0 +1,39 @@
+#
+# Bug #51920: InnoDB connections in lock wait ignore KILL until timeout
+#
+-- source include/not_embedded.inc
+-- source include/have_innodb_plugin.inc
+
+CREATE TABLE bug51920 (i INT) ENGINE=InnoDB;
+INSERT INTO bug51920 VALUES (1);
+
+BEGIN;
+SELECT * FROM bug51920 FOR UPDATE;
+
+connect (con1,localhost,root,,);
+
+connection con1;
+--send
+UPDATE bug51920 SET i=2;
+
+connection default;
+let $wait_condition =
+  SELECT COUNT(*)=1 FROM information_schema.processlist
+  WHERE INFO="UPDATE bug51920 SET i=2";
+-- source include/wait_condition.inc
+
+SELECT ID FROM INFORMATION_SCHEMA.PROCESSLIST
+WHERE INFO="UPDATE bug51920 SET i=2"
+INTO @thread_id;
+
+KILL @thread_id;
+let $wait_condition =
+  SELECT COUNT(*)=0 FROM information_schema.processlist WHERE ID=@thread_id;
+-- source include/wait_condition.inc
+
+connection con1;
+-- error ER_QUERY_INTERRUPTED
+reap;
+connection default;
+DROP TABLE bug51920;
+-- disconnect con1