fix test suite warnings

fix test suite warnings

fix a handful of warnings that were emitting but not raising,
usually because they were inside an "expect_warnings" block.

modify "expect_warnings" to always use "raise_on_any_unexpected"
behavior; remove this parameter.

Fixed issue in semi-private ``await_only()`` and ``await_fallback()``
concurrency functions where the given awaitable would remain un-awaited if
the function threw a ``GreenletError``, which could cause "was not awaited"
warnings later on if the program continued. In this case, the given
awaitable is now cancelled before the exception is thrown.

Change-Id: I33668c5e8c670454a3d879e559096fb873b57244