Switch to decorators.idempotent_id

test.idempotent_id is being kept temporary to migrate
to new lib interface. Now idempotent_id is available as Tempest stable
interface decorators and all plugins tests using the old decorator
should be switched to new interface.

In future, Once all plugins are switched to new decorator Tempest
will remove the test.idempotent_id

Change-Id: I9c7ffec7e65ea2cd3c9807fac3909317d8923c85
Related-Bug: 1616913
diff --git a/tempest_horizon/tests/scenario/test_dashboard_basic_ops.py b/tempest_horizon/tests/scenario/test_dashboard_basic_ops.py
index e4a13d9..67ed227 100644
--- a/tempest_horizon/tests/scenario/test_dashboard_basic_ops.py
+++ b/tempest_horizon/tests/scenario/test_dashboard_basic_ops.py
@@ -17,8 +17,8 @@
 from six.moves.urllib import request
 
 from tempest import config
+from tempest.lib import decorators
 from tempest.scenario import manager
-from tempest import test
 
 import ssl
 import sys
@@ -133,7 +133,7 @@
         return ((sys.version_info[0] == 2 and sys.version_info[2] >= 9) or
                 (sys.version_info[0] == 3))
 
-    @test.idempotent_id('4f8851b1-0e69-482b-b63b-84c6e76f6c80')
+    @decorators.idempotent_id('4f8851b1-0e69-482b-b63b-84c6e76f6c80')
     def test_basic_scenario(self):
         creds = self.os.credentials
         self.check_login_page()