r1.12-rc1 cherry-pick request: Update to new RBE toolchain with Clang 8.0.0 r340178. (#22904)

* Update to new toolchain with Clang 8.0.0 r340178.
 - Also update bazel to 0.16.1 because the new toolchain image requires it.

PiperOrigin-RevId: 216590129

* Fix lstm_test&layer_norm_lstm_test w/ Clang 8.0.0

PiperOrigin-RevId: 216475683

* Fix lite/kernels:add_test for Clang 8.0.0

PiperOrigin-RevId: 216455772

* Fix mul_test with Clang 8.0.0

PiperOrigin-RevId: 216570443

* Add tf.contrib.estimator.python to exclude path