#tf-buildcop Fix test timeout.
#tf-buildcop Fix test timeout.

Error:
```
//tensorflow/core/data/service/snapshot:snapshot_stream_writer_checkpoint_test TIMEOUT in 3 out of 3 in 96.0s
  Stats over 3 runs: max = 96.0s, min = 66.2s, avg = 79.4s, dev = 12.4s
  tensorflow/core/data/service/snapshot/snapshot_stream_writer_checkpoint_test/test.log
  tensorflow/core/data/service/snapshot/snapshot_stream_writer_checkpoint_test/test_attempts/attempt_1.log
  tensorflow/core/data/service/snapshot/snapshot_stream_writer_checkpoint_test/test_attempts/attempt_2.log
```
