fix cp stageout to always create 775 directories

The cp stageout plugin creates all the needed new directories,
but if they are multiple levels deep, only the last one will
get the desired permission bits of 775. Fix that so that all
newly created directories have the same 775 permissions.
Merge pull request #4846 from hufnagel/cp-umask

fix cp stageout to always create 775 directories