Merge pull request #6000 from ctiller/optionalize_roundrobin

BUILD

Makefile

binding.gyp

build.yaml

config.m4

gRPC.podspec

grpc.gemspec

package.json

package.xml

src/core/ext/lb_policy/grpclb/load_balancer_api.c

src/core/ext/lb_policy/grpclb/load_balancer_api.h

.../ext/lb_policy/grpclb/proto/grpc/lb/v0/load_balancer.pb.c

.../ext/lb_policy/grpclb/proto/grpc/lb/v0/load_balancer.pb.h

src/core/ext/lb_policy/pick_first/pick_first.c

src/core/ext/lb_policy/round_robin/round_robin.c

src/core/lib/client_config/lb_policy_registry.c

src/core/lib/client_config/lb_policy_registry.h

src/core/lib/surface/init.c

src/core/plugin_registry/grpc_plugin_registry.c

src/core/plugin_registry/grpc_unsecure_plugin_registry.c