Improve `sh' task action error handling:

Handle exit status code in Remote#execute.

lib/producer/core/errors.rb

@@ -1,8 +1,9 @@
 module Producer
   module Core
-    Error                 = Class.new(StandardError)
-    ConditionNotMetError  = Class.new(Error)
-    RecipeEvaluationError = Class.new(StandardError)
-    TaskEvaluationError   = Class.new(RecipeEvaluationError)
+    Error                       = Class.new(StandardError)
+    ConditionNotMetError        = Class.new(Error)
+    RecipeEvaluationError       = Class.new(StandardError)
+    TaskEvaluationError         = Class.new(RecipeEvaluationError)
+    RemoteCommandExecutionError = Class.new(Error)
   end
 end