Get an existing retention policy.

    database
        Name of the database for which the retention policy was
        defined.

    name
        Name of the retention policy.

    CLI Example:

    .. code-block:: bash

        salt '*' influxdb.get_retention_policy metrics default

def get_retention_policy(database, name, **client_args):
    '''
    Get an existing retention policy.

    database
        Name of the database for which the retention policy was
        defined.

    name
        Name of the retention policy.

    CLI Example:

    .. code-block:: bash

        salt '*' influxdb.get_retention_policy metrics default
    '''
    client = _client(**client_args)

    try:
        return next((p for p in client.get_list_retention_policies(database)
                     if p.get('name') == name))
    except StopIteration:
        return {}