This reverts commit 79759fea, reversing
changes made to dc36f4df.

Change shebangs to `#!/usr/bin/env python` instead of
`#!/usr/bin/env python2.7`.

Update run_tests/*.py to use six based isomorphisms and print function
from __future__ module.

The client binary can be built with 'bazel build //tools/grpcz:grpcz_client' and
can be invoked with bazel-bin/tools/grpcz/grpcz_client --server SERVER_ADDR:PORT
You can see the stats page at http://localhost:8000/grpcz

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.

This should have been a part of 06dea573.