Do not restart language worker processes as part scripthost restarts

[pragnagopa]

LangaugeWorkers are initialized inside scriptHost
https://github.com/Azure/azure-functions-host/blob/dev/src/WebJobs.Script/Host/ScriptHost.cs#L262

This results in language worker processes restarting when scripthost restart for example, when user updates function code.

[mhoeger]

This also causes functions host to crash on file save when debugging node functions: #3543

[alrod]

Customer report:
https://stackoverflow.com/questions/53599053/azure-process-terminates-when-javascript-function-is-changed

[fabiocav]

@jeffhollan @pragnagopa @mhoeger Assigning this as a P1, but this issue should be addressed by the placeholder work being done, so it would make sense to close this in favor of the issues tracking that work if we want to go that route.

[ahmedelnably]

Closing per @fabiocav comment