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

BUILD

CMakeLists.txt

Makefile

build.yaml

doc/connectivity-semantics-and-api.md

gRPC-Core.podspec

grpc.gemspec

include/grpc/impl/codegen/gpr_slice.h

include/grpc/impl/codegen/slice.h

package.xml

src/core/lib/iomgr/ev_epoll_linux.c

src/core/lib/support/string.h

src/core/lib/support/tmpfile.h

src/csharp/Grpc.Auth/Grpc.Auth.csproj

src/csharp/Grpc.Core.Tests/Grpc.Core.Tests.csproj

src/csharp/Grpc.Core/Grpc.Core.csproj

src/csharp/Grpc.Core/NativeDeps.targets

.../Grpc.Examples.MathClient/Grpc.Examples.MathClient.csproj

.../Grpc.Examples.MathServer/Grpc.Examples.MathServer.csproj

src/csharp/Grpc.Examples.Tests/Grpc.Examples.Tests.csproj