scripts: Don't terminate current session in terminate-psql-sessions.

This is a prep commit. Running terminate-psql-sessions command on
docker-zulip results in the script exiting with non-zero exit status
2. This is because the current session also gets terminated while
running terminate-psql-sessions command. To prevent that from happening
we don't terminate the session created by terminate-psql-sessions.

scripts/setup/terminate-psql-sessions

@@ -32,5 +32,6 @@ SELECT pg_terminate_backend(s.pid)
     WHERE
         s.datname IN ($tables)
         AND r.rolname = CURRENT_USER
-        AND (s.usename = r.rolname OR r.rolsuper = 't');
+        AND (s.usename = r.rolname OR r.rolsuper = 't')
+        AND s.pid <> pg_backend_pid();
 EOF