Fail to open the web page after deploying image (Python/.NET Core) to Azure App Service with custom location

[v-ruizh]

OS: All
Build Version: 1.13.0

Repro Steps:

1. Open one Python project(Django/Flask) and add Docker files for this project in VS Code.
2. Right click Dockerfile -> Build Image.
3. Right click this image in image view -> Push -> Azure -> Select a registry to push.
4. Right click the image in registry view -> Deploy Image to Azure App Service -> Create a new app service with a custom location.
5. When done, click "Open Site" button in the notification.
6. Check whether the web page can be opened successfully.

Expect:
Succeed to open the web page.

Actual:
Fail to open the web page with the “upstream request timeout” message.

More Info:

1. This issue also reproduces when deploying a .NET Core MVC project with port 5000, does not reproduce with port 80.
2. This issue does not reproduce when deploying an Express App.
3. This issue does not reproduce for non-custom location.