Tests in wsrep suite can't run without InnoDB, but suite is not configured to use it

Test suite 'wsrep' heavily depends on the presence of InnoDB. If I add a minimal test to the suite, e.g.

$ cat suite/wsrep/t/t1.test

show variables like 'wsrep%';

It fails complaining

150207 20:42:54 [Warning] WSREP: error executing 'SET GLOBAL innodb_disallow_writes=1': 1193 (Unknown system variable 'innodb_disallow_writes'). Was mysqld built with --with-innodb-disallow-writes ?

If the whole suite's logic relies on the presence of InnoDB, it should be configured this way – either via combinations or via the config file.