Implement condition DSL negated test prefix (no_*)

* Allow no_* to be used for every tests in condition DSL:
  condition { no_has_env :shell, '/bin/sh' };
* Modify Test constructor to accept negated: named argument, implement
  #negated? and #pass?;
* Rename #success? to #verify in all test classes.

lib/producer/core/condition/dsl.rb

@@ -13,6 +13,9 @@ module Producer
             define_method(keyword) do |*args|
               @tests << klass.new(@env, *args)
             end
+            define_method("no_#{keyword}") do |*args|
+              @tests << klass.new(@env, *args, negated: true)
+            end
           end
         end