bdev: Add a TODO and a pylint silence

A piece of old code in bdev.py uses a for loop over a single variable
because we can 'break' out of the loop or exit on the 'else' path. This
is not a nice usage of the for loop, it should be converted to a
standard if...elif...else structure.

In the meantime we silence a warning from pylint (it is actually
invalid, IMHO) and add a TODO.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Olivier Tharan <olive@google.com>