Refactor the startFlipper function
Refactor the startFlipper function

Summary:
Refactors `startFlipper` function in headless flipper into three different functions.

`earlyExitActions`: Before the dispatcher is called on the store and will exit if the user arguments are one which are meant to terminate the process.
`exitActions`: This function will be called after the dispatcher is called and will exit if the user arguments are one which are meant to terminate the process.
`storeModifyngActions`: It involves business logic which updates the store based on the user arguments.

Reviewed By: passy

Differential Revision: D15556130

fbshipit-source-id: 9d1b035525e613bb2b75454fa4fd6c193993b530

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