Update callouts.py for python3
Update callouts.py for python3

Specify that python3 should be used in the script.

Signed-off-by: Matt Spinler <c000c989d08c98662d98f15448f11de169feb92d@us.ibm.com>
Change-Id: I826f31b376dae484c52a244c9fb7dc9fb8f917c1

openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging