Support NBO for DROP TABLE in Galera

I got this from a MariaDB user:

I have executed test on Galera Cluster. Notice the result of the test. DML operations are blocked for the duration of the DROP statement. If this was huge table with drop taking over 2-3min we might have serious issue on top loaded DCs.

+----------------+

| version() |

+----------------+

| 11.1.2-MariaDB |

+----------------+

SESSION1
MariaDB [testdb]> drop table bigtable1;
Query OK, 0 rows affected (8.487 sec)

SESSION2
MariaDB [testdb]> insert into t1 values (2,'Test123');
Query OK, 1 row affected (7.282 sec)

SESSION3
MariaDB [test]> insert into t values (2,'Test');
Query OK, 1 row affected (6.177 sec)

SESSION4
MariaDB [(none)]> show processlist;
+----+-------------+-----------+--------+---------+------+---------------------------+-------------------------------------+----------+
| Id | User | Host | db | Command | Time | State | Info | Progress |
+----+-------------+-----------+--------+---------+------+---------------------------+-------------------------------------+----------+
| 1 | system user | | NULL | Sleep | 632 | wsrep aborter idle | NULL | 0.000 |
| 2 | system user | | NULL | Sleep | 632 | closing tables | NULL | 0.000 |
| 7 | system user | | NULL | Sleep | 80 | After apply log event | NULL | 0.000 |
| 9 | system user | | NULL | Sleep | 631 | wsrep applier idle | NULL | 0.000 |
| 10 | system user | | NULL | Sleep | 69 | wsrep applier committed | NULL | 0.000 |
| 12 | root | localhost | testdb | Query | 3 | Waiting for certification | insert into t1 values (2,'Test123') | 0.000 |
| 13 | root | localhost | testdb | Query | 4 | closing tables | drop table bigtable1 | 0.000 |
| 15 | root | localhost | test | Query | 1 | Waiting for certification | insert into t values (2,'Test') | 0.000 |
| 16 | root | localhost | NULL | Query | 0 | starting | show processlist | 0.000 |
+----+-------------+-----------+--------+---------+------+---------------------------+-------------------------------------+----------+
9 rows in set (0.000 sec)