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

CONTRIBUTING.md

Makefile

README.md

build.json

etc/roots.pem

include/grpc/grpc_security.h

src/core/security/security_context.c

src/node/examples/route_guide.proto

src/python/src/grpc/_adapter/fore.py

src/python/src/grpc/_adapter/rear.py

src/ruby/bin/interop/interop_client.rb

templates/Makefile.template

test/cpp/interop/interop_test.cc

tools/distpackages/build_deb_packages.sh

tools/dockerfile/grpc_build_deb/Dockerfile

tools/dockerfile/grpc_ruby_deb/Dockerfile

tools/dockerfile/grpc_ruby_deb/README.md

tools/run_tests/tests.json

vsprojects/vs2013/Grpc.mak