Description of problem:
The current Fedora 25 systemd will error if you start a unit with the line 
"ExecStart=/sbin/runuser -l user -c "/usr/bin/vncserver -localhost %i"" when you have edited the user details.

Version-Release number of selected component (if applicable):
Draft Fedora 25 Administrators Guide Edition 1

How reproducible:
Every time

Steps to Reproduce:
1. Implement a vncserver as detailed in https://docs.fedoraproject.org/en-US/Fedora/25/html/System_Administrators_Guide/ch-TigerVNC.html
2. Edit the respective /etc/systemd/system/vncserver@.service file by replacing the user details
3. Start the server using "systemctl start vncserver@:1.server" or as a no root user "sudo systemctl start vncserver@:1.server" and it fails 

Actual results:
/sbin/runuser can only be run by root

Expected results:
vnc server starts

Additional info:
I think the problem is created as the vncserver@.service file set the process owner as defined in the line "User=<USER>". When I have set that to a non-root user name the file errors.

The standard file line "ExecStart=/usr/bin/vncserver %i" works fine. The errata seems to be a hangover from the old file structure.