mariadb/mysql-test/suite/wsrep

* 'wsrep' suite is designated for tests which do not require a multi-node
  galera cluster.

* As these tests are specific to wsrep-related functionalities, they must skip
  on server built without wsrep patch (vanilla). (-DWITH_WSREP=OFF)
  See : include/have_wsrep.inc, include/have_wsrep_enabled.inc, not_wsrep.inc