Lately, after we increased number of jobs, infra started to experience
network traffic issues due to us downloading registries. This
per-nodepool cache should help and also speed up actual gate.
Change-Id: I621a9c91e4508ef208a28137a736fd8468388219
Depends-On: I527d32f9b43dabb7640bfb056e2bf828b7c1dfa9