Add asyncio.TimeoutError as an exit exception

Add asyncio.TimeoutError as an exit exception

Added ``asyncio.exceptions.TimeoutError``,
``asyncio.exceptions.CancelledError`` as so-called "exit exceptions", a
class of exceptions that include things like ``GreenletExit`` and
``KeyboardInterrupt``, which are considered to be events that warrant
considering a DBAPI connection to be in an unusable state where it should
be recycled.

Fixes: #6592
Change-Id: Idcfa7aaa2d7660838b907388db9c6457afa6edbd