Add pg-drop script to sonic filesystem (sonic-net#1583)

- What I did
Added 'pg-drop' to the files system of SONiC

- How I did it
Add 'scripts/pg-drop' to setup.py file

- How to verify it
Check that 'pg-drop' script exists in /usr/local/bin/pg-drop

Signed-off-by: Andriy Yurkiv <ayurkiv@nvidia.com>

setup.py

@@ -108,6 +108,7 @@
         'scripts/nbrshow',
         'scripts/neighbor_advertiser',
         'scripts/pcmping',
+        'scripts/pg-drop',
         'scripts/port2alias',
         'scripts/portconfig',
         'scripts/portstat',