Added symmetric and asymmetric vaults.
    
    The vault plugin has been modified to support symmetric and asymmetric
    vaults to provide additional security over the standard vault by
    encrypting the data before it's sent to the server. The encryption
    functionality is implemented using the python-cryptography library.
    
    https://fedorahosted.org/freeipa/ticket/3872
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>