This ensures that the test is not flaky after lots of iterations.
Along the way, change newhope_test.cc to C++.
Change-Id: I4ef139444b8c8a98db53d075105eb6806f6c5fc7
Reviewed-on: https://boringssl-review.googlesource.com/8110
Reviewed-by: Adam Langley <agl@google.com>
