tablet picker: use partial result from GetTabletMap if it is available. check for cell before cellsAlias to reduce number of topo errors.
tablet picker: use partial result from GetTabletMap if it is available.
check for cell before cellsAlias to reduce number of topo errors.

Signed-off-by: deepthi <3f83f38ad2e2ddcc47e21eb12a05ce66eb4cf525@planetscale.com>

mahak/vitess,vitessio/vitess,tinyspeck/vitess,vitessio/vitess,vitessio/vitess,mahak/vitess,tinyspeck/vitess,tinyspeck/vitess,tinyspeck/vitess,vitessio/vitess,mahak/vitess,vitessio/vitess,tinyspeck/vitess,vitessio/vitess,mahak/vitess,vitessio/vitess,mahak/vitess,mahak/vitess,mahak/vitess,vitessio/vitess,tinyspeck/vitess,mahak/vitess,tinyspeck/vitess