Python 3.3 reached its end-of-life 2017-09-29:

  https://www.python.org/dev/peps/pep-0398

Closes https://github.com/neovim/neovim/issues/14586

The current guidance for install Python packages is to use

    python -m pip install <package_name>

Instead of

    pip install <package_name>

This ensures that one is using the version of pip that is tied to the
environment's interpreter (and, thusly, its packages).  This has [been
endorsed by a core
maintainer](https://snarky.ca/why-you-should-use-python-m-pip/) as
being the recommended way to invoke pip.

As there currently are a few places where the old invocation was used,
attempt to bring them in line.

Fixes #14234

fixes #13415

fixes #13700

- If the shada file is set with shada option n, use it.
- If the shadafile is NONE, it does not check for file read/write access.
- If the shada file does not exist, try to create it.

CPAN tests are unreliable on Windows.
CI does the same to reduce flaky,slow builds.

Problem: ruby#Detect() and node#Detect() don't return a [prog, err] pair
which means callers must special-case them.

Solution: align their return signatures with the perl/pythonx providers.