Add check_db_integrity script to setup.py (#1828)

The script was added in the PR #1785 which did not add this script to the setup.py script.
Added the check_db_integrity script to setup.py.

Author: vaibhavhd

setup.py

@@ -135,7 +135,8 @@
         'scripts/watermarkcfg',
         'scripts/sonic-kdump-config',
         'scripts/centralize_database',
-        'scripts/null_route_helper'
+        'scripts/null_route_helper',
+        'scripts/check_db_integrity.py'
     ],
     entry_points={
         'console_scripts': [