Move resource.py to core/

Change-Id: I0f36a5e61ff0ef14d08165c9c184acdf2d6e6901
diff --git a/selftest/resource_test.py b/selftest/resource_test.py
index ecbeb24..0b9550e 100755
--- a/selftest/resource_test.py
+++ b/selftest/resource_test.py
@@ -6,9 +6,8 @@
 import shutil
 import atexit
 import _prep
-from osmo_gsm_tester.core import config, log, util
+from osmo_gsm_tester.core import config, log, util, resource
 from osmo_gsm_tester.core.schema import generate_schemas
-from osmo_gsm_tester import resource
 
 workdir = util.get_tempdir()