Tests probably shouldn't require write authorization to the collections being ingested into

[psFried]

Say you have a test:

tests:
  coyote/anvils/does_the_thing_when_anvil_is_dropped:
    - ingest:
        collection: acmeCo/anvils
        documents: [...]
    - verify:
        collection: coyote/anvils/drops
        documents: [...]

Flow currently checks that the role coyote/anvils/does_the_thing_when_anvil_is_dropped has write capability to acmeCo/anvils. I think we should consider easing that restriction to only require read access, which would make it possible to write tests for derivations that read from collections you don't have write access to.