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

Change-Id: I9aec6c55ccd71894182057d36e0025b69925d314
diff --git a/src/osmo_gsm_tester/pcu_sysmo.py b/src/osmo_gsm_tester/pcu_sysmo.py
index 55d6f53..e907367 100644
--- a/src/osmo_gsm_tester/pcu_sysmo.py
+++ b/src/osmo_gsm_tester/pcu_sysmo.py
@@ -19,7 +19,8 @@
 
 import os
 import pprint
-from . import log, config, util, template, process, pcu
+from .core import log, config, util, template, process
+from . import pcu
 
 class OsmoPcuSysmo(pcu.Pcu):