[SSSD] RFC: intg: Add basic user/group/membership change tests

[Nikolai Kondrashov]

Hi everyone,

I'm working on adding more LDAP integration tests upstream and here are some
first results: basic user/group/membership addition/removal tests.

Admittedly they're very basic, although needed some research first.

What I'd like to get is some feedback and also a solution to one issue, which
seems external: these tests break memory cache integration tests (traceback
attached). Lukas thinks this might be related to
https://fedorahosted.org/sssd/ticket/2726

I'm posting the patch here to help him investigate, as well.

Thank you.

Nick