Added a script and config for bringing interop test to kokoro

Serialize running of perf, switch back to -f for consistent event counts

Run perf benchmarks in parallel

Store cython-level call in grpc.Call

Should only do host-->:authority if there is no :authority

Make latency traces more useful

Add flamegraphs to index.html

Packet Coalescing - Core

Cleanup files during processing

Update protobuf version used for nanopb compiler

This allows inspecting c-level properties of the call after completion.

Use pre-existing script for flamegraph generation

Use shell to redirect a few big files

Fix command line

Added Pylint to sanity tests for the grpc package alone.

Most pylint rules are disabled and for each disabled rule, there is a related TODO added to the .pylintrc.

Fix path

Pylint is only enabled for "grpcio/grpc" package,
and various specific checks that currently fail are disabled,
each with a respective TODO item in the .pylintrc file.