Merge remote-tracking branch 'upstream/master' into service_config

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

doc/environment_variables.md

doc/interop-test-descriptions.md

gRPC-Core.podspec

grpc.gemspec

include/grpc++/impl/codegen/server_context.h

include/grpc++/test/server_context_test_spouse.h

include/grpc/support/alloc.h

package.xml

src/core/ext/client_config/subchannel.c

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

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

src/core/ext/load_reporting/load_reporting.h

src/core/ext/load_reporting/load_reporting_filter.c

src/core/ext/transport/chttp2/transport/chttp2_plugin.c