Add redis dependencies by default

[dpwrussell]

I'm opening this issue to track the addition of redis requirements to the build.

I am doing it like this: https://github.com/dpwrussell/omero-web-docker/tree/redis temporarily, but I believe this should be an optino on the underlying ansible role instead of specific to this docker install.

[joshmoore]

Do you want to go ahead and open a PR to add redis-requirements so we get a step closer to a full solution?