break the habit of throwing away the actually useful error messages

The lines that help dignose a problem is almost never the first one that
just states "there was an error". The explanation of the error follows
in the next lines. So don't quit immediately after the first error-line,
but wait what the command has to tell and log/print the whole info.

Change-Id: I2a4b3470b4b66ed37fa5e5a34d452c548d24b965
Reviewed-on: https://gerrit.libreoffice.org/5861Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Reviewed-by: Thorsten Behrens <tbehrens@suse.com>
Tested-by: Thorsten Behrens <tbehrens@suse.com>

postprocess/signing/signing.pl

@@ -208,17 +208,16 @@ sub execute     #11.07.2007 10:02
 {
     my $commandline = shift;
     my $result = "";
-
-      print "$commandline\n" if ($debug);
-      open(PIPE, "$commandline 2>&1 |") || die "Error: Cant open pipe!\n";
-      while ( $result = <PIPE> ) {
-          print LOG "$result" if ($opt_log);        # logging
-          if ( $result =~ /SignTool Error\:/ ) {
-            close PIPE;
-              print_error( "$result\n" );
-          } # if error
-      } # while
-      close PIPE;
+    my $errorlines = "";
+
+    print "$commandline\n" if ($debug);
+    open(PIPE, "$commandline 2>&1 |") || die "Error: Cannot execute '$commandline' - $!\n";
+    while ( $result = <PIPE> ) {
+        print LOG "$result" if ($opt_log);
+        $errorlines .= $result if ($result =~ /SignTool Error\:/);
+    } # while
+    close PIPE;
+    print_error( "$errorlines\n" ) if ($errorlines);
 }   ##execute
 
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