'Create a cell mapping for cell0.
cell0 is used for instances that have not been scheduled to any cell.
This generally applies to instances that have encountered an error
before they have been scheduled.
This command creates a cell mapping for this special cell which
requires a database to store the instance data.
Returns 0 if cell0 created successfully or already setup.'

@args('--database_connection', metavar='<database_connection>', help='The    database    connection    url    for    cell0.    This    is    optional.    If    not    provided,    a    standard    database    connection    will    be    used    based    on    the    main    database    connection    from    the    Nova    configuration.')
def map_cell0(self, database_connection=None):

    try:
        self._map_cell0(database_connection=database_connection)
    except db_exc.DBDuplicateEntry:
        print(_('Cell0    is    already    setup'))
    return 0
