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.

features/tests/negated_test.feature

@@ -0,0 +1,44 @@
+@sshd
+Feature: negated test prefix (no_)
+
+  Scenario: prefixed test fails when non-prefixed test is successful
+    Given a recipe with:
+      """
+      target 'some_host.test'
+
+      task :successful_test do
+        condition { has_env :shell }
+
+        echo 'successful_test'
+      end
+
+      task :negated_test do
+        condition { no_has_env :shell }
+
+        echo 'negated_test'
+      end
+      """
+    When I successfully execute the recipe
+    Then the output must contain "successful_test"
+    And the output must not contain "negated_test"
+
+  Scenario: prefixed test fails when non-prefixed test is failing
+    Given a recipe with:
+      """
+      target 'some_host.test'
+
+      task :failing_test do
+        condition { has_env :inexistent_var }
+
+        echo 'failing_test'
+      end
+
+      task :negated_test do
+        condition { no_has_env :inexistent_var }
+
+        echo 'negated_test'
+      end
+      """
+    When I successfully execute the recipe
+    Then the output must not contain "failing_test"
+    And the output must contain "negated_test"