Before this change, running Python tests individually required
building a tox environment via the run_tests script and then specifying
long environment variables to filter out just the test we wanted to run
(and then we wouldn't be able to get the output on interrupt, nor would
we have an easy way of determining the PID of the process for debugger
attachment). Now invoking the build_python.sh script creates a workable
python virtual environment that includes all necessary libraries and
tests (s.t. running a single test is now possible by just knowing the
module name). This does not change existing supported means of running
tests (e.g. through run_tests.py).

An additional way of running individual tests has been introduced.
Following invocation of `./tools/run_tests/build_python.sh` (or
run_tests.py), one may invoke

  ./$VENV/bin/python -m $TEST_MODULE_NAME

and acquire a single running process that *is* the test process (rather
than a parent of the process). $VENV is the virtual environment name
specified to `build_python.sh` (defaults to `py27`) and
$TEST_MODULE_NAME is what it says on the tin.

Moves all tests into a separate package. This does not change existing
supported means of running tests (e.g. through run_tests.py).

Fix memory leak, fix error.c refcount reporting

Build objective-c examples as part of automatic tests

Add a maybe-temporary way for apps to clear the channel cache

fix for working with compressed data. Fixes #6746.

Use open-source defaults to propagate Python plugin configuration

Fix bug with override_server flag in run_interop_tests.py

Dont create errors redundently in chttp2_transport.c

implemented eventfd_check_availability

Fix Python server interop spec noncompliance

PHP: fix shutdown hang issue

Updated git clone URL

fixed size_t format string

Changed default string type to be str

Build experimental nugets with dotnet CLI

Make transport-level errors be reflected in status messages on calls

Re-enable two Node credentials tests

This impacts the following APIs:
  Metadata: Key is always a str, Value is bytes for binary metadata,
    str otherwise
  Call Details: str type
  gRPC method: str type
  hostname/target: str type

Also fix spelling mistakes in the spec itself.

Convert windows dll filename to bytes

Lowered six dependency version to 1.5.2

Build ObjC examples in travis

Removed _connectivity_channel tests