cbuild: Use a specified uid for FDO_USER
Previously, useradd would create a user with an id of 1000, however that can be problematic if you try to run the image in a different enviornment, such as locally, as the uid could class with the local users on the system.
I thought of choosing a random uid, but that wouldn't be reproducible™
Thus, always create a user with uid and gid of 10042
Edited by Jordan Petridіs