Create users in server-common pre hook
    
    The ipaapi user was created in the server package but referenced by a
    config file in the server-common package. The server-common package can
    be installed without the server package. This caused an error
    
       Unknown user 'ipaapi'
    
    with systemd-tmpfiles --create. The users are now created in the
    server-common package.
    
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexey Slaykovsky <alexey@slaykovsky.com>