rename default.conf to defaults.conf

Change-Id: I0928ed306b0ca9b173dac092c77a9c6986714803
diff --git a/src/osmo_gsm_tester/config.py b/src/osmo_gsm_tester/config.py
index 68bbd13..4abdebb 100644
--- a/src/osmo_gsm_tester/config.py
+++ b/src/osmo_gsm_tester/config.py
@@ -174,7 +174,7 @@
     return config
 
 def get_defaults(for_kind):
-    defaults = read_config_file('default.conf', if_missing_return={})
+    defaults = read_config_file('defaults.conf', if_missing_return={})
     return defaults.get(for_kind, {})
 
 class Scenario(log.Origin, dict):