Bring luks_add_key and luks_remove_key back into devicelibs.crypto.
    
    In order to include these in pycryptsetup we had to create yet
    another duplicate copy of execWithRedirect. This patch brings them
    back into anaconda so we can easily modify them if needed until
    the day when pycryptsetup has this functionality. It also allows us
    to redirect the output to someplace useful for debugging.