use osmo_init_logging2(), fix regression test memleaks

Particularly gbproxy_test.c had various mem leaks, which (will) show up with
gcc (Debian 7.3.0-15) 7.3.0 address sanitizer. Fix those leaks to verify that
we don't have memleaks in the production code.

Change-Id: Ia4204c8b3d895b42c103edecb61b99d3d22bd36f
diff --git a/src/gprs/gtphub_main.c b/src/gprs/gtphub_main.c
index 197c5e3..a1a2c1d 100644
--- a/src/gprs/gtphub_main.c
+++ b/src/gprs/gtphub_main.c
@@ -346,7 +346,7 @@
 	signal(SIGUSR2, &signal_handler);
 	osmo_init_ignore_signals();
 
-	osmo_init_logging(&gtphub_log_info);
+	osmo_init_logging2(osmo_gtphub_ctx, &gtphub_log_info);
 
 	vty_info.copyright = gtphub_copyright;
 	vty_init(&vty_info);