Fix `:creator` & `:commenter` traits in plans factory

[aaronskiba]

Changes proposed in this PR:

• Prior to this change, rather than assigning the desired role to the newly created plan, executing create(:plan, :creator... or create(:plan, :commenter... would create a second new plan.
• This code change makes sure that when the creator or commenter trait is specified, it is applied to the first created plan and that a second one is not created.