Add copybara rules to export C++ test code.
Add copybara rules to export C++ test code.

PiperOrigin-RevId: 219166541
Change-Id: Ieebadaed4096eb48f00fba663e1c76fb41438078

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor