Feature: add a "bypass" environment variable

[abeforgit]

Sometimes when debugging/developing around the cache, it can be handy to disable it without messing up the dispatcher configuration. A sort of "bypass" environment variable which would cause the cache to "always miss" would be a nice-to-have.

[erikap]

@abeforgit Isn't it an option to temporarily link resource as cache in dispatcher like

services:
  dispatcher:
    image: semtech/mu-dispatcher:2.1.0-beta.2
    volumes:
      - ./config/dispatcher:/config
    links:
      - resource:cache   

[abeforgit]

Ooh cool idea! Ill give it a try, thanks!