func azure functionapp publish $appname doesn't work if you change the container image

Try the following. It creates a new FunctionApp using Azure CLI and attempts to change an appsetting and the container image.

```
$Location = "West US 2"
$ResourceGroupName = "mytestfunc"
$PlanName = "mytestfuncplan"
$StorageName = "mytestfuncstore"
$FunctionAppName = $ResourceGroupName

az group create -l $Location -n $ResourceGroupName
az appservice plan create -g $ResourceGroupName -n $PlanName --is-linux
az storage account create -n $StorageName -g $ResourceGroupName -l $Location --sku Standard_LRS
az functionapp create -g $ResourceGroupName -n $FunctionAppName -s $StorageName -p $PlanName --os-type linux --runtime dotnet
az functionapp config appsettings set -n $FunctionAppName -g $ResourceGroupName --setting
az webapp config container set -i "" -n $FunctionAppName -g $ResourceGroupName
```

> NOTE: the FOO=bar was to change the worker runtime and the image is to an image I know works in Azure (published via ARM template which worked)

when I attempt to publish a function app, I get this:

```
PS > func azure functionapp publish $FunctionAppName
Getting site publishing info...
Creating archive for current directory...
Uploading archive...
Upload completed successfully.
Functions in tyleonha-test:
PS >
```

Note that no functions show up. There should be 1 HttpTrigger template which I verified works.

Start with the `func azure functionapp publish` entry point and reproduce the documented Azure CLI setup, including the app setting and container image change. Compare the publish result with the expected single HttpTrigger function; done means publishing after changing the container image makes the function appear and work.

Written by the indexing model from the issue text.