I was looking for the same and managed to fix it like this:
Hostname Configuration Method for App VM
To modify the hostname in an application virtual machine (appvm), you can use the following approach:
Open the /rw/config/rc.local configuration file
Add the command: hostnamectl hostname [new-hostname]
Example: hostnamectl hostname mystery-machine
To check the result restart the AppVM and run hostnamectl in the commandline.
Additional configuration options include:
Changing the icon name
Changing the chassis type
Modifying deployment settings
Updating location information
Run hostnamectl --help to see the above options.