FM-1509 Update for Future_Parser Testing

The feature being used landed here: https://github.com/puppetlabs/beaker/pull/262
The env var is from the comments in the PR.
I'm currently using the config file setting to (also discussed in the linked PR) enable future parser testing currently in the module's CI. However I do think maintaining all those duplicate config files is both unmaintainable in the long run for both CI and dev usage.
I think modules should allow things like optional feature flags that they want to sometimes test against to be configurable (like future parser, or strict variables, or whatever else comes in the future), I think environment variables are a natural fit for toggling such things.
I don't particularly care what env var you guys decide on, so long as it's consistent across all modules.