Fix connectivity tests under Windows

More robust port_server version checking

Enable `pip` caching

Fix broken udp_server_test, by adding exec_ctx to read_cb

Node interop custom_metadata

Add verbosity to Python `run_tests.py` output.

unref slice before cancel

Type conversion fixes to make GCC 5.2.0 happy

Fix thread stuck problem on Mac

Add auth interop test support to run_interop_tests.py

Add ruby server to run_interop_tests.py

Upport changes from 0.11 release branch.

This is in preparation for the eventual refactoring of the run_tests.py
system.

Removed a pair of racy Node tests

Use sys.executable instead of hard coding python binary string

This is necessary to get the right binary on Windows