Don't write LIBARCHIVE.creationtime attribute in tar.gz archive entries

Fixes #2586

tycho-p2-director-plugin/src/main/java/org/eclipse/tycho/plugins/tar/TarGzArchiver.java

@@ -129,6 +129,7 @@ private TarArchiveEntry createTarEntry(File tarRootDir, File source) throws IOEx
             tarEntry.setMode(FilePermissionHelper.toOctalFileMode(attrs.permissions()));
         }
         tarEntry.setModTime(source.lastModified());
+        tarEntry.setCreationTime(null); // tar cannot handle 'LIBARCHIVE.creationtime' attributes 
         return tarEntry;
     }