Revert changes to staging for performance tests and increased rate limit

- Reverted the Gunicorn worker number to 5 (this should be investigated
further on a well baselined system to compare)
- Enabled REDIS
- Increased the rate limit to 400 req/sec as using early testing
yesterday 450+ was being achieved

manifest-api-staging.yml

@@ -1,7 +1,6 @@
 ---
 
 inherit: manifest-api-base.yml
-command: scripts/run_app_paas.sh gunicorn -c /home/vcap/app/gunicorn_config.py --error-logfile /home/vcap/logs/gunicorn_error.log -w 6 -b 0.0.0.0:$PORT application
 services:
   - notify-aws
   - notify-config