Raise to 4 the shard counts of...

Raise to 4 the shard counts of //third_party/tensorflow/contrib/{factorization:kmeans_test,linear_optimizer:sdca_estimator_test}

These tests were getting flaky timeouts when run under asan, sometimes taking
longer than the 5 minute timeout.  Increasing the shard count to 4 seems to be
sufficient to cause them not to time out.

PiperOrigin-RevId: 183470183