Merge pull request #5799 from richardkchapman/joinmulti-stress

HPCC-11332 Recategorize joinmulti test as a stress test

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>

testing/ecl/joinmulti.ecl

@@ -1,3 +1,4 @@
+//class=stress
 unsigned numgroups := 10000;
 unsigned largeGroupSize := 500;
 unsigned largeGroupFreq := 30;