oeqa/sdk/maturin: be less picky in the list_python test

oeqa/sdk/maturin: be less picky in the list_python test

The test assumed that maturin would only find a single Python binary, in
/usr/bin/python3*.

However in eSDKs with buildtools a Python is shipped with the SDK, so
the test failed.

Generalise the test so that it runs python3 and obtains its path and
version, and then verifies that path and and version are found by
Maturin. This means we're not assuming a single Python, or the paths, or
that the Python is CPython.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>