fixup: bsc: Add testscase & infra to validate Osmux support BTS<->BSC

The per-BTS VTY command 'osmux (on|off|only)' was added to osmo-bsc.git
recently, and is not available in -latest yet.  Use it conditionally.

Change-Id: Id501d3f4b5eb18b096d8baffcb5f38e583f7a3d8
Fixes: I6e82eb9d995de988b812001e1c4cf6923509de66
diff --git a/bsc/BSC_Tests.ttcn b/bsc/BSC_Tests.ttcn
index d4a7b20..6418b4b 100644
--- a/bsc/BSC_Tests.ttcn
+++ b/bsc/BSC_Tests.ttcn
@@ -1273,13 +1273,15 @@
 	f_wait_oml(bts_idx, "connected", 5.0);
 
 	/* Set up BTS with VTY commands: */
-	f_vty_enter_cfg_bts(BSCVTY, bts_idx);
-	if (g_osmux_enabled_bts) {
-		f_vty_transceive(BSCVTY, "osmux on");
-	} else {
-		f_vty_transceive(BSCVTY, "osmux off");
+	if (Misc_Helpers.f_osmo_repo_is("nightly")) {
+		f_vty_enter_cfg_bts(BSCVTY, bts_idx);
+		if (g_osmux_enabled_bts) {
+			f_vty_transceive(BSCVTY, "osmux on");
+		} else {
+			f_vty_transceive(BSCVTY, "osmux off");
+		}
+		f_vty_transceive(BSCVTY, "end");
 	}
-	f_vty_transceive(BSCVTY, "end");
 }
 
 function f_init_bts_and_check_sysinfo(integer bts_idx := 0,