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/pcap_recorder.py b/src/osmo_gsm_tester/pcap_recorder.py
index e0f0098..a9ba3a7 100644
--- a/src/osmo_gsm_tester/pcap_recorder.py
+++ b/src/osmo_gsm_tester/pcap_recorder.py
@@ -19,7 +19,7 @@
 
 import os
 
-from . import log, process
+from .core import log, process
 
 class PcapRecorder(log.Origin):