Merge branch 'master' of github.com:grpc/grpc into core_creds_api_change

examples/python/helloworld/greeter_server.py

include/grpc++/client_context.h

include/grpc++/support/time.h

src/core/tsi/test_creds/server1.pem

src/cpp/client/client_context.cc

src/csharp/Grpc.IntegrationTesting/data/server1.pem

src/node/test/data/server1.pem

src/php/tests/data/server1.pem

src/python/grpcio/grpc/framework/interfaces/face/face.py

src/python/grpcio_test/grpc_interop/credentials/server1.pem

src/python/grpcio_test/grpc_test/credentials/server1.pem

src/ruby/spec/testdata/server1.pem

test/core/end2end/data/server1_cert.c

test/cpp/end2end/end2end_test.cc