MAN: sssctl debug level
    
    Use tools specific reference to debug level explanation in sssctl
    man page.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/3085
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    (cherry picked from commit 1af143e258985b286bfe29ce942a4173e4eae8e0)