Target cell filter.
A scheduler hint of ‘target_cell’ with a value of a full cell name may be
specified to route a build to a particular cell.  No error handling is
done as there’s no way to know whether the full path is a valid.
- 
class TargetCellFilter
 
Bases: nova.cells.filters.BaseCellFilter
Target cell filter.  Works by specifying a scheduler hint of
‘target_cell’. The value should be the full cell path.
- 
filter_all(cells, filter_properties)
 
Override filter_all() which operates on the full list
of cells...