Create core directory to contain most of code not in object classes used by tests

Change-Id: I9aec6c55ccd71894182057d36e0025b69925d314
diff --git a/selftest/resource_test.py b/selftest/resource_test.py
index cdfe021..f399e20 100755
--- a/selftest/resource_test.py
+++ b/selftest/resource_test.py
@@ -6,7 +6,8 @@
 import shutil
 import atexit
 import _prep
-from osmo_gsm_tester import config, log, resource, util
+from osmo_gsm_tester.core import config, log, util
+from osmo_gsm_tester import resource
 
 workdir = util.get_tempdir()