Merge branch 'master' into node_bind_port_zero

.gitignore

src/node/common.js

src/node/examples/math_server.js

src/node/interop/empty.proto

src/node/interop/interop_client.js

src/node/interop/interop_server.js

src/node/interop/messages.proto

src/node/interop/test.proto

src/node/main.js

src/node/package.json

src/node/surface_client.js

src/node/surface_server.js

src/node/test/interop_sanity_test.js

src/node/test/math_client_test.js

src/node/test/surface_test.js

tools/dockerfile/grpc_base/Dockerfile

tools/dockerfile/grpc_cxx/Dockerfile

tools/dockerfile/grpc_php/Dockerfile

tools/dockerfile/grpc_php_base/Dockerfile

tools/dockerfile/grpc_ruby/Dockerfile