Make it possible to actually set concurrency

We were reading it from the top-level of config.json, but it's being
filtered out from the yaml and not being included, so we always have the
default of 2.

I'd like to try going to 1 to help investigate something else, and now
it will be possible.

Also, now that we're able to set this value, we need to make sure it's
not a string.

Author: maxjacobson

lib/cc/engine/analyzers/engine_config.rb

@@ -22,7 +22,7 @@ def languages
         end
 
         def concurrency
-          config.fetch("concurrency", 2)
+          config.fetch("config", {}).fetch("concurrency", 2).to_i
         end
 
         def mass_threshold_for(language)

spec/cc/engine/analyzers/engine_config_spec.rb

@@ -158,4 +158,16 @@
       expect(engine_config.include_paths).to eq(["/tmp"])
     end
   end
+
+  describe "concurrency" do
+    it "coerces to a number" do
+      engine_config = CC::Engine::Analyzers::EngineConfig.new({
+        "config" => {
+          "concurrency" => "45",
+        },
+      })
+
+      expect(engine_config.concurrency).to eq(45)
+    end
+  end
 end