build-remote.pl: Pass /dev/null as SSH's stdin

Otherwise it will set the parent's stdin to non-blocking mode, causing
the subsequent read of the set of inputs/outputs to fail randomly.
That's insane.

scripts/build-remote.pl.in

@@ -197,7 +197,7 @@ REQ: while (1) {
         $hostName = $machine->{hostName};
         last REQ if
             openSSHConnection($hostName) &&
-            system("ssh $hostName @sshOpts nix-builds-inhibited >/dev/null 2>&1") != 0;
+            system("ssh $hostName @sshOpts nix-builds-inhibited < /dev/null > /dev/null 2>&1") != 0;
 
         warn "unable to open SSH connection to $hostName, trying other available machines...\n";
         $machine->{enabled} = 0;