plan randomly fails because changeset is not yet findable on aws service

[eatwithforks]

we need to either retry or sleep 1 to avoid this to randomly fail.

in realize.rb

        plan = stack.plan
        if plan.nil?
          raise Error::StackPlanNotFound,
            "Failed to locate plan for stack `#{name}`"
        end

[eatwithforks]

@chrisroberts