Use RBE for remote caching on GCE (#659)

* Use RBE for remote caching on GCE.

This also changes the anti-cache-poisoning strategy back to using
--remote_default_platform_properties with a cache-silo-key instead of
appending the platform key to the URL of the cache, because the latter
is not supported by gRPC caching.

* Seems like grpcs:// is not yet supported by Bazel 0.25, use --tls_enabled instead
1 file changed