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/test.rb

@@ -3,9 +3,18 @@ module Producer
     class Test
       attr_reader :env, :arguments
 
-      def initialize(env, *arguments)
+      def initialize(env, *arguments, negated: false)
         @env        = env
         @arguments  = arguments
+        @negated    = negated
+      end
+
+      def negated?
+        @negated
+      end
+
+      def pass?
+        verify ^ negated?
       end
     end
   end