vault: move client-side code to the module level
    
    Move client-side code from the vault class to module-level functions.
    
    This will make it possible to move the code to ipaclient without the vault
    class bits.
    
    https://fedorahosted.org/freeipa/ticket/4739
    
    Reviewed-By: David Kupka <dkupka@redhat.com>