- make closures know where they should be executed (eg, on a workqueue,
  or a combiner, or on an exec_ctx)
- this allows removal of a large number of trampoline functions that
  were appearing whenever we used combiners, and should allow for a much
  easier interface to combiner locks

Check and fail if user provides a metadata key starting with :

Fix jwt verifier

Cleanup and speedup sanity tests

Fix Python artifact build

Update interop html template location

Ruby: show error class and message instead of unknown

Clean up tools/run_tests directory

Better qps_json_driver message when QPS_WORKERS env is missing

- Initializes grpc correctly in the JWT utils.
- Make the email mapping work with the new service accounts produced by
  Google IAM.
- Adding check for email issuers where the issuer has to be the subject as well.
- Implementing portable version of memrchr.

Change grpcio_tools to grpcio-tools

allow disable core_list setting and override qps server in benchmarks

Support --exclude in run_tests_matrix.py

This should address the difference in how we ask users to install
grpcio-tools and the files the user ends up downloading from PyPI.

Allow running many runs per test without flooding the logs

Reintroduce test timeouts eliminated by mistake

Get wrapped endpoint's fd in secure_endpoint's endpoint_get_fd

Fix metrics server

v1.0.x manual upmerge

Add Python Client to Test Negative HTTP2 Conditions

Documentation for the new tests can be found https://github.com/grpc/grpc/blob/master/doc/negative-http2-interop-test-descriptions.md