Stdout/stderr logs during worker init not sent to app insights

[ejizba]

Repro steps

Provide the steps required to reproduce the problem:

1. Clone this repo: https://github.com/ejizba/func-stdout-file-load

2. Run npm install

3. Deploy to a flex consumption Node.js app

4. Hit the http trigger

5. Run the following query in app insights:

   traces
   | where message startswith "stdout log" or message startswith "rpc log"

Expected behavior

These are the logs I see on windows consumption:

Actual behavior

These are the logs I see on flex:

Related information

This is a big deal because the workers send app startup errors over stdout/stderr (the suggested workaround for #9360) and app startup errors are quite common/frustrating with the new programming models. I suspect this issue might be related to the host split work, so I feel it's important we figure this out before moving the host split to non-flex skus.