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.rb

@@ -14,7 +14,7 @@ module Producer
 
       def met?
         return !!@return_value if @tests.empty?
-        @tests.each { |t| return false unless t.success? }
+        @tests.each { |t| return false unless t.pass? }
         true
       end