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.

spec/support/tests_helpers.rb

@@ -1,9 +1,9 @@
 module TestsHelpers
   def test_ok
-    double('test', success?: true)
+    double('test', pass?: true)
   end
 
   def test_ko
-    double('test', success?: false)
+    double('test', pass?: false)
   end
 end