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

Change-Id: I9aec6c55ccd71894182057d36e0025b69925d314
diff --git a/src/osmo_ms_driver/__main__.py b/src/osmo_ms_driver/__main__.py
index a752c37..a4276d9 100644
--- a/src/osmo_ms_driver/__main__.py
+++ b/src/osmo_ms_driver/__main__.py
@@ -22,7 +22,7 @@
 from .cdf import cdfs
 from .starter import BinaryOptions, MobileTestStarter
 from .test_support import imsi_ki_gen
-from osmo_gsm_tester import log, util
+from osmo_gsm_tester.core import log, util
 from osmo_gsm_tester import ms_osmo_mobile
 
 # System modules