MT#55283 preserve stderr on test fail

Change-Id: I157213a2e396212f14fbaac82441011e180fe3a3

perl/NGCP/Rtpengine/AutoTest.pm

@@ -325,6 +325,8 @@ sub terminate {
 
 	print "hint: rtpe stdout output is at $rtpe_stdout\n";
 	print "hint: rtpe stderr output is at $rtpe_stderr\n";
+	print "last lines:\n";
+	system(qw(tail -n 40), $rtpe_stderr);
 
 	die "error: $msg\n";
 }