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/tests/has_env.rb

@@ -2,7 +2,7 @@ module Producer
   module Core
     module Tests
       class HasEnv < Test
-        def success?
+        def verify
           env.remote.environment.has_key? arguments.first.to_s.upcase
         end
       end

lib/producer/core/tests/has_file.rb

@@ -2,7 +2,7 @@ module Producer
   module Core
     module Tests
       class HasFile < Test
-        def success?
+        def verify
           env.remote.fs.has_file? arguments.first
         end
       end