Merge branch 'master' into tsi_grpc

BUILD

CMakeLists.txt

Makefile

bazel/grpc_build_system.bzl

build.yaml

doc/environment_variables.md

gRPC-Core.podspec

grpc.gemspec

include/grpc/impl/codegen/grpc_types.h

package.xml

src/core/ext/filters/client_channel/channel_connectivity.c

...rs/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c

src/core/lib/iomgr/nameser.h

src/core/lib/iomgr/port.h

src/core/lib/surface/alarm.c

src/core/lib/surface/call.c

src/core/lib/surface/channel_ping.c

src/core/lib/surface/completion_queue.c

src/core/lib/surface/completion_queue.h

src/core/lib/surface/server.c