Make it easy to switch to nightly libtpu and jax #10533

Job	Run time
get-torch-commit	1s
Build PyTorch/XLA / build	34m 35s
Build docs / build-docs	1m 37s
TPU tests / tpu-test	45m 56s
CPU tests / test (benchmark_tests)	8m 55s
CPU tests / test (python_tests, xla_op1)	18m 39s
CPU tests / test (python_tests, xla_op2)	6m 41s
CPU tests / test (python_tests, xla_op3)	9m 15s
CPU tests / test (python_tests, torch_mp_op)	13m 0s
CPU tests / test (cpp_tests, cpp_tests1)	5m 48s
CPU tests / test (cpp_tests, cpp_tests2)	11m 17s
	2h 35m 44s

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