Updated the call to the user provider so it creates a system user

By adding ‘system true’ to the call, this user will now be created with
‘useradd -r’ which makes the user have a low UID (usually below 500)
and treads this used as a system user.
Merge pull request #128 from svanharmelen/system_user_fix

Updated the call to the user provider so it creates a system user