Add JH_ENV as the switch in env.rb

What does this MR do and why?

What: Add JH_ENV as switch in env.rb
Why: We need to add new logic on JH side; I think the env variable should be a good switch about JH logic.
For example, in update.rb.

type = current_release.ee? ? 'ee' : 'ce'

This is no ce edition on JH side, we may add an if expression for JH logic here.

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/cc @daveliu