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/gb_proxy_main.c b/src/gprs/gb_proxy_main.c
index 1416ff5..04143bb 100644
--- a/src/gprs/gb_proxy_main.c
+++ b/src/gprs/gb_proxy_main.c
@@ -275,7 +275,7 @@
 	signal(SIGUSR2, &signal_handler);
 	osmo_init_ignore_signals();
 
-	osmo_init_logging(&gprs_log_info);
+	osmo_init_logging2(tall_bsc_ctx, &gprs_log_info);
 
 	vty_info.copyright = openbsc_copyright;
 	vty_init(&vty_info);