Merge github.com:grpc/grpc into simpler-cq

.gitignore

.travis.yml

include/grpc/grpc_security.h

src/core/iomgr/iomgr.c

src/core/iomgr/socket_windows.c

src/core/security/credentials.c

src/core/security/credentials.h

src/core/security/google_default_credentials.c

src/core/security/json_token.c

src/core/security/json_token.h

src/core/surface/server.c

src/node/health_check/health.js

src/node/health_check/health.proto

src/node/src/server.js

src/node/test/health_test.js

src/python/requirements.txt

src/python/src/.gitignore

src/python/src/grpc/_adapter/.gitignore

src/python/src/grpc/_cython/.gitignore

src/python/src/grpc/_cython/README.rst