cache: add default logger

[alecholmez]

Signed-off-by: Alec Holmes [email protected]

[alecholmez]

@snowp here's that default logger I promised, I pulled out the nil logger checks in the cache since we don't need them anymore. I used uber's zap logger since it maps nicely to what we setup and it's the fastest structured logger which we probably need for a system like this.

If we don't want a defaulted logger I can just make this a no-op

[alecholmez]

@snowp should be good to go, default is just a noop that logs out nothing. This keeps current logging behavior

[alecholmez]

@snowp can we merge this in before we cut a v0.10? Just want to clean up the PRs

[snowp]

Thanks!