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/bts_oc2g.py b/src/osmo_gsm_tester/bts_oc2g.py
index d1f80b7..0cebc09 100644
--- a/src/osmo_gsm_tester/bts_oc2g.py
+++ b/src/osmo_gsm_tester/bts_oc2g.py
@@ -19,7 +19,8 @@
 
 import os
 import pprint
-from . import log, config, util, template, process, remote, pcu_oc2g, bts_osmo
+from .core import log, config, util, template, process, remote
+from . import pcu_oc2g, bts_osmo
 
 class OsmoBtsOC2G(bts_osmo.OsmoBts):
 ##############