Internal Server Error - https://<app_name>.azurewebsites.net/admin/host/keys

_From @handeeadiguzel on February 12, 2018 15:1_

> Please provide us with the following information:
> ---------------------------------------------------------------

### OS and Browser
> Windows & Chrome

### Repro steps
>
1. Create function app from azure portal
2. Change runtime version to beta (2.0.11415.0 (beta))
2. Enable deployment slots

Host keys are gone (portal doesn't show them anymore). And cannot add new keys.

### Any error messages
>

> Internal Server Error - https:///admin/host/keys
> Session Id: 40a3ea0af19f42ceae950c973d66b770
>
> Timestamp: 2018-02-12T14:42:19.631Z

### Mention any other details that might be useful.

_Copied from original issue: Azure/azure-functions-ux#2334_