Consider using with no assign

[DudeNr33]

Steps

• Add a ChangeLog entry describing what your PR does.
• Write a good description on what the PR does.

Description

As noted in this comment the consider-using-with message was not triggered if a call like open() was used outside an assignment expression.
So while this triggered the message:

filehandle = open("foo")

this did not:

open("foo")

This is because calls returning context managers were only checked for in the visit_assign method.
The logic was fixed.
Some new findings in the code base now emerged, which were fixed (or suppressed, for the functional test files).

Type of Changes

	Type
✓	🐛 Bug fix

Related Issue

None.

[coveralls]

Coverage decreased (-0.009%) to 91.712% when pulling 84cb34d on DudeNr33:consider-using-with-no-assign into 318f1af on PyCQA:master.

[Pierre-Sassoulas]

Looks pretty clean, thank you. It also detected two more problems in pylint which is a good sign !