[Python 3]exec to eval where exec(" var = ...")

Summary:
All exec() with (var = ...)
exec() with (import ... ) or with (self.var = ..) or just with (function()) should work out of the box.
If not worked as expected, they could be grouped and put into other diff s.

Reviewers: PyKolab Developers, sicherha

Reviewed By: PyKolab Developers, sicherha

Differential Revision: https://git.kolab.org/D3638