ttcn3/lib/testlib.py: implement the concept of test case groups

Change-Id: I687c221e4a6c7232290509cb11a3158d72b9c2c3
diff --git a/sysmocom/ttcn3/suites/ttcn3_bts_tests/ttcn3_bts_tests.py b/sysmocom/ttcn3/suites/ttcn3_bts_tests/ttcn3_bts_tests.py
index 4382454..7f0b24f 100755
--- a/sysmocom/ttcn3/suites/ttcn3_bts_tests/ttcn3_bts_tests.py
+++ b/sysmocom/ttcn3/suites/ttcn3_bts_tests/ttcn3_bts_tests.py
@@ -6,7 +6,9 @@
 tenv.test_import_modules_register_for_cleanup(testlib)
 from testlib import run_ttcn3
 
-ttcn3_test_execute="BTS_Tests.control"
+ttcn3_test_groups = [
+    'BTS_Tests',
+]
 
 hlr_dummy = tenv.hlr()
 mgw_dummy = tenv.mgw()
@@ -46,4 +48,4 @@
 osmocon.start()
 
 testdir = os.path.dirname(os.path.realpath(__file__))
-run_ttcn3(tenv, testdir, bts, osmocon, nat_rsl_ip, ttcn3_test_execute)
+run_ttcn3(tenv, testdir, bts, osmocon, nat_rsl_ip, ttcn3_test_groups)