Make the soft-reboot available in the SONiC image on master (sonic-net#1681)

Make the soft-reboot available in the SONiC image on master

What I did
Add soft-reboot to build package

How I did it
Add "soft-reboot" to the package list of sonic-utility/setup.py

How to verify it
Build a SONiC image, load the image to DUT and check if soft-reboot is available.

Author: sujinmkang

setup.py

@@ -120,6 +120,7 @@
         'scripts/route_check_test.sh',
         'scripts/vnet_route_check.py',
         'scripts/sfpshow',
+        'scripts/soft-reboot',
         'scripts/storyteller',
         'scripts/syseeprom-to-json',
         'scripts/tempershow',