CBQE-2178: fix exclude_group param in testrunner

Change-Id: I49fef6958300f035561aa03cf9cbcbd99de4e062
Reviewed-on: http://review.couchbase.org/35197
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>