set workload = 'olap'; can not repeat, but set workload = 'oltp' can;

[linuxgood1230]

vitess@host set workload = 'olap';
Query OK, 0 rows affected (0.00 sec)

vitess@host set workload = 'olap';
ERROR 1105 (HY000): vtgate: http://host:22170/: unsupported construct: set

- exit, reconnect
vitess@host set workload = 'oltp';
Query OK, 0 rows affected (0.00 sec)

vitess@host set workload = 'oltp';
Query OK, 0 rows affected (0.00 sec)

[dweitzman]

This looks like #3977

[Akkadius]

You also can't switch to 'oltp' once you have set workload = 'olap'; until you disconnect/reconnect