Merge github.com:grpc/grpc into direct-calls

examples/php/route_guide/run_route_guide_client.sh

src/core/ext/census/tracing.c

src/php/lib/Grpc/BaseStub.php

src/php/tests/interop/interop_client.php

src/php/tests/unit_tests/CallCredentials2Test.php

tools/run_tests/run_tests.py