[cp] HACK: sleep before sign

On Windows, with 16x parallel build, build-nocheck target fails,
because it tries to sign a file that is already in use (gengal).

Change-Id: Ic582334f2c02f5e38f49d048fc0425025ffeee41

postprocess/signing/signing.pl

@@ -41,6 +41,7 @@ my @args        = ();
 my @files_to_sign = ();
 
 #### main #####
+sleep(120);
 $myname = script_id();
 if ( $#ARGV < 2 ) {
     usage();