Add Bind Host to Functions Emulator inspect argument

[collindever]

Description

Returns host from the functionsEmulator::getinfo() function in case no arg was passed and binds inspect to the same host the functions emulator is running on.

This is useful for running on Docker containers where services need to bind to 0.0.0.0. Issue was also raised in the now archived cloud-functions-emulator repo here googlearchive/cloud-functions-emulator#325 and a similar fix is proposed in their pull request here. googlearchive/cloud-functions-emulator#326

Scenarios Tested

With no host passed in the firebase.json debug binds to default localhost sample test output for the command firebase emulators:start --inspect-functions

i  emulators: Starting emulators: functions
⚠  functions: You are running the functions emulator in debug mode (port=9229). This means that functions will execute in sequence rather than in parallel.
✔  functions: Using node@8 from host.
✔  functions: Emulator started at http://localhost:5001
i  functions: Watching "/home/node/app/functions" for Cloud Functions...
>  Debugger listening on ws://localhost:9229/bed89267-5c07-47c1-87fc-41154f0e40d3

Adding the following to firebase.json

    "emulators": {
        "functions": {
          "host": "0.0.0.0"
        }
      }

and running the same command as above results in ...

i  emulators: Starting emulators: functions
⚠  functions: You are running the functions emulator in debug mode (port=9229). This means that functions will execute in sequence rather than in parallel.
✔  functions: Using node@8 from host.
✔  functions: Emulator started at http://0.0.0.0:5001
i  functions: Watching "/home/node/app/functions" for Cloud Functions...
>  Debugger listening on ws://0.0.0.0:9229/6f51ba0f-d092-4cb4-87e2-e0da4392bbf4

Confirmed I could connect to debugger with vsCode and the following launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "node",
            "request": "attach",
            "name": "Attach",
            "address": "0.0.0.0",
            "port": 9229,
            "restart": true,
            "skipFiles": [
                "<node_internals>/**"
            ]
        }
}

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[coveralls]

Coverage decreased (-0.05%) to 65.569% when pulling 24a1d09 on collindever:bind-functions-inspect-to-host into 51523c0 on firebase:master.

[samtstern]

@collindever thanks for the contribution! Seems like a reasonable change. Could you:

a) Take a look at the CLA (you only need to do this once and it covers all Google repos)
b) Update the PR description to fill in the missing sections.

[collindever]

@googlebot I signed it!
@samtstern thanks for taking a look, I appreciate your time! Let me know if you need anything else from me.

[googlebot]

CLAs look good, thanks!

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[samtstern]

@collindever this is great thank you! Will merge once the CI passes.