In the EAP 7 installer it was possible to inline this password into the script itself. This seems not to be the case for EAP 8 even though there is a place in the script where it looks like to be possible to set this password:

<admin-user username="admin" adminPassword=""/> 

however changing this attribute doesn't do anything.

IIUC the user should not be editing the script, so this issue shouldn't really have much of an impact, but IMO if we have the attribute in the script, it should do what is expected. 
One possible resolution could be to just get rid of the attribute