TOOLS: Call "exec" for sss_debuglevel
This suggestion came from Lukáš Slebodník. The advantage of calling
"exec" is to avoid forking another child of the process.
Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>