Emulator triggers firewall warnings on every startup

[jribbink]

Instructions

Prevent flow-emulator from creating a firewall dialog every time it runs.

Issue To Be Solved

Currently, the flow-emulator listens on 0.0.0.0 which causes a firewall dialog to appear every time the emulator runs. This can be quite frustrating when the emulator is not run as a standalone, but rather automated by something such as the Flow JS Testing framework.

(Optional): Suggest A Solution

Listen on 127.0.0.1 loopback address instead of 0.0.0.0. This solution is only valid if there is no existing purpose for the emulator to accept any incoming connections and only local ones.

If there is a reason to listen for incoming connections, this could be done as a command line flag.

(Optional): Context

@onflow/flow-js-testing spawns a new child process of the flow-emulator every time it runs a test. This means that when running tests on their local machine, developers will get hit with a new firewall dialog every time a test runs (i.e. on Mac "do you want to accept incoming connections" and likely something similar on Windows)