BUILD: Add a config option for sssd user, own private directories as the user
    
    Adds a new configure-time option that lets you select the user to run
    SSSD as. The default is 'root' for backwards compatibility.
    
    The directories the deamon stores its private data at are also created
    as owned by this user during install time.
    
    Reviewed-by: Pavel Reichl <preichl@redhat.com>
    Reviewed-by: Simo Sorce <simo@redhat.com>