Only log TPU topology from the master worker
Currently logs at mesh initialization time on the client side has lots of duplicated logs: https://gist.githubusercontent.com/jysohn23/fda8cc58d47cc03e1ab22fb91ea1b33b/raw/c31b14b2a19ee64ad56ba09e46fb21834bc31ced/v3-32-resnet50-real-data-numworkers64-n1standard64-bs256-bf16-sharded.txt. Will do similar around `XrtComputationClient` constructor too.
