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/stp_osmo.py b/src/osmo_gsm_tester/stp_osmo.py
index 5a7f0d3..500c5da 100644
--- a/src/osmo_gsm_tester/stp_osmo.py
+++ b/src/osmo_gsm_tester/stp_osmo.py
@@ -20,7 +20,8 @@
 import os
 import pprint
 
-from . import log, util, config, template, process, pcap_recorder
+from .core import log, util, config, template, process
+from . import pcap_recorder
 
 class OsmoStp(log.Origin):