secret: Introduce virSecretObjListAdd* and virSecretObjListRemove
    
    Add the functions to add/remove elements from the hashed secret obj list.
    These will replace secret_driver functions secretAssignDef and secretObjRemove.
    
    The virSecretObjListAddLocked will perform the necessary lookups and
    decide whether to replace an existing hash entry or create a new one.
    This includes setting up the configPath and base64Path as well as being
    able to support the caller's need to restore from a previous definition
    in case something goes wrong in the caller.