check_fts_update_log: Fix psycopg2 arguments.

* Fixes passing a string argument rather than an actual Python
  argument.
* Switches to hardcoding the database to connect to rather than the
  user, so this check can be run as an arbitrary user.

puppet/zulip/files/nagios_plugins/zulip_postgres_appdb/check_fts_update_log

@@ -25,7 +25,7 @@ def report(state, num):
     print("%s: %s rows in fts_update_log table" % (state, num))
     exit(states[state])
 
-conn = psycopg2.connect("user=zulip")
+conn = psycopg2.connect(database="zulip")
 cursor = conn.cursor()
 
 cursor.execute("SELECT count(*) FROM fts_update_log")