Only pull images once per day to avoid pull rate limits

We now authenticate but that's not enough since we are only allowed 200 pulls every 6 hours.

• We do 4 pulls for a single module build
• We have 20 docker-based test modules in platform
• We currently run 3 configs for docker-latest

So that's 20 * 4 * 3 = 240 > 200 for each branch. We build 2 or 3 branches...