Simplify Remote::Environment with factory method:

* Implement .new_from_string factory class method;
* Rename private method #parse_from_string as class method
  .string_to_hash;
* Remove argument kind detection logic in constructor.

lib/producer/core/remote.rb

@@ -45,7 +45,7 @@ module Producer
       end
 
       def environment
-        Environment.new(execute 'env')
+        Environment.new_from_string(execute 'env')
       end
     end
   end