MDEV-15149 Assert upon concurrent creating / querying sequences

Problem was that sequence_insert closed and reopened the like table
without proper locking.  Fixed by ensuring that the like table is
not reopened in sequence_insert

mysql-test/suite/sql_sequence/concurrent_create.test

@@ -0,0 +1,40 @@
+--source include/have_sequence.inc
+--source include/have_innodb.inc
+
+#
+# MDEV-15149 Assorted assertion failures upon concurrent creating / querying
+# sequences (same test case)
+#
+
+CREATE SEQUENCE s1 ENGINE=InnoDB;
+CREATE SEQUENCE s2 ENGINE=InnoDB;
+
+--connect (con1,localhost,root,,test)
+--send CREATE TABLE s3 LIKE s2;
+
+--connection default
+CREATE SEQUENCE s4 ENGINE=InnoDB;
+SELECT * from s1 WHERE start_value IN (SELECT start_value FROM s2);
+
+--connection con1
+--reap
+
+# Cleanup
+--disconnect con1
+--connection default
+DROP SEQUENCE s1, s2, s3, s4;
+
+#
+# Check prepared statements
+#
+
+CREATE SEQUENCE s1 ENGINE=InnoDB;
+PREPARE stmt FROM "CREATE TABLE s2 LIKE s1";
+execute stmt;
+drop table s2;
+execute stmt;
+drop table s2;
+execute stmt;
+select * from s2;
+DROP SEQUENCE s1, s2;
+