osutil: force SIG_DFL before resending terminating signal

The go runtime won't always reinstall the default signal handler on the
SIGTERM path, so it's possible the signal won't terminate the process.
Instead, force SIG_DFL for the signal.

pkg/osutil/interrupt_unix.go

@@ -68,6 +68,7 @@ func HandleInterrupts() {
 		if pid == 1 {
 			os.Exit(0)
 		}
+		setDflSignal(sig.(syscall.Signal))
 		syscall.Kill(pid, sig.(syscall.Signal))
 	}()
 }