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/simple_loop.py b/src/osmo_ms_driver/simple_loop.py
index 29a4b5b..373fa20 100644
--- a/src/osmo_ms_driver/simple_loop.py
+++ b/src/osmo_ms_driver/simple_loop.py
@@ -15,7 +15,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from osmo_gsm_tester import log
+from osmo_gsm_tester.core import log
 
 import os
 import selectors