Bug Description:
When automember and memberof are enabled, if a user is member of a group
because of an automember rule. Then when the group is deleted,
memberof updates the member (to update 'memberof' attribute) that
trigger automember to reevaluate the automember rule and add the member
to the group. But at this time the group is already deleted.
Chaining back the failure up to the top level operation the deletion
of the group fails

Fix Description:
The fix consists to check that if a automember rule tries to add a user
in a group, then to check that the group exists before updating it.

https://pagure.io/389-ds-base/issue/50282

Reviewed by: ?

Platforms tested: F29

Flag Day: no

Doc impact: no