Comment 3 for bug 1428424

In neutron project there are approx 281 of occurrences of contextlib.nested, so fixing all of these in a single patch will be cumbersome for review.

I will be submitting this change in a series of patches to ease the review process, where I'll add hacking rules for the same in the last patch.

These patches will only remove the use of contextlib.nested from the neutron code base and is not intended to remove use of nested with statements.