It was causing git to ignore everything within src/core

Also updates the version of grpcio_test. Now that grpcio and its tests
are in different project packages, the version numbers should be kept in
sync.

Conditionally runs the tests depending on the availability of Python
versions (because Travis is the worst).

The app doesn’t do anything yet

By default don't re-run tests that have already run successfully, to
reduce latency between making a change and seeing if it fixed the last
thing that you were trying to fix.

Allows us to collect profiles of the open source build using gprof.

This is a tool for collecting coverage reports from our tests and
combining them with the open-source tool 'lcov'.