Implement client side cluster resolving (#910)
* Implement client side cluster resolving
Unit tested the client side cluster resolving for now, but will merge with server side tests in following PR. Also ran google `pyformat`.
Coverage report
```
Name Stmts Miss Cover Missing
--------------------------------------------------------------------------
/pytorch/xla/torch_xla_py/xla_dist.py 122 10 92% 12-13, 50, 139-142, 185, 198, 228, 266, 281
/pytorch/xla/torch_xla_py/xla_dist_test.py 170 4 98% 203, 224-225, 468
--------------------------------------------------------------------------
TOTAL 292 14 95%
```
