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

Change-Id: I9aec6c55ccd71894182057d36e0025b69925d314
diff --git a/selftest/template_test.py b/selftest/template_test.py
index f4f1bd5..747d508 100755
--- a/selftest/template_test.py
+++ b/selftest/template_test.py
@@ -5,7 +5,7 @@
 import sys
 import os
 
-from osmo_gsm_tester import template, log
+from osmo_gsm_tester.core import template, log
 
 log.set_level(log.C_CNF, log.L_DBG)