[rspec] Created test objects must be part of the same organization

Currently, a test setup like this creates TWO organizations:

let(:group) { create(:group) }
let(:project} { create(:pproject) }

This can be fixed by:

let(:group) { create(:group) }
let(:project} { create(:pproject, group: organization) }

But that would require a lot of changes to our test setup.

So we will create a "Common Organization" that will be assigned if no explicit organization is assigned