Force tests to be non-interactive

--- a/test/test_dropbear.py
+++ b/test/test_dropbear.py
@@ -23,7 +23,7 @@
 	args = opt.dropbear.split() + [
 		"-p", LOCALADDR + ":" + opt.port, # bind locally only
 		"-r", opt.hostkey,
-		"-F", "-E",
+		"-F", "-E", "-s",
 		]
 	print("subprocess args: ", args)