[rails] Detect workers for Iodine

+------------------------+---------+------+------+-----+-----+-------+--------------+
|             branch_name|plaintext|update|  json|   db|query|fortune|weighted_score|
+------------------------+---------+------+------+-----+-----+-------+--------------+
|                  master|   127557| 12167| 88459|24399|19880|  15784|          1480|
|rails/iodine-set-workers|   158915| 15101|111481|28795|21691|  18549|          1767|
+------------------------+---------+------+------+-----+-----+-------+--------------+

frameworks/Ruby/rails/rails-iodine.dockerfile

@@ -24,4 +24,4 @@ ENV RAILS_ENV=production_postgresql
 ENV PORT=8080
 ENV REDIS_URL=redis://localhost:6379/0
 CMD service redis-server start && \
-    bundle exec iodine
+    bundle exec iodine -w $(ruby config/auto_tune.rb | grep -Eo '[0-9]+' | head -n 1)