This PR also adds a new testutils directory with a fake client and a
channel which supports a timed receive operation. In follow up PRs, we
can move other common test stuff like the fake server etc to this
directory and cleanup more tests.
Fields are added in: https://github.com/grpc/grpc-proto/pull/64
Other changes:
- Move XDSConfig from internal to balancer
- Later we will add a separate config for CDS balancer
- generate service_config.pb.go and test with json generated from proto message
This resolver doesn't do much at this point, except returning an empty
address list and a hard-coded service config which picks the xds
balancer with a round_robin child policy.
Also moved the xdsConfig struct to the xds/internal package and exported
it as LBConfig, so that both the resolver and the balancer packages can
make use of this.
