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

Change-Id: I9aec6c55ccd71894182057d36e0025b69925d314
diff --git a/selftest/suite_test.py b/selftest/suite_test.py
index 115d76e..c4dd5bf 100755
--- a/selftest/suite_test.py
+++ b/selftest/suite_test.py
@@ -2,7 +2,8 @@
 import os
 import _prep
 import shutil
-from osmo_gsm_tester import log, suite, config, report, util
+from osmo_gsm_tester.core import log, config, util
+from osmo_gsm_tester import suite, report
 
 config.ENV_CONF = './suite_test'