Manage pool of flavors instead of destroying immediately after use

[itsjoekent]

• Define via environment variables how many flavors can be executed at once.
• Maintain a stack of flavors, push flavors up to the top of the stack when they get hit. If a flavor reaches the bottom of the stack, destroy it.
• Provide an asynchronous interface for the proxy module to find out what port a flavor is using

Open Questions

• Concurrency, at what point do we spin up more instances of a flavor?
• If we have a max of 10 active flavors, and all 10 of those are in the middle of a request, and an 11th request comes in, what should we do? (Queue the spin up?)