Use ddt.named_data decorator to avoid random test names

There are few tests that generate random test names because
random parameters are given to the ddt.data  decorator.

In the ddt version number 1.6.0 there is a possibility to
determine the name of the tests without relying on the
given values. I think this could be a good solution for
the randomly generated names.

Change-Id: Iaf39f4a83e383fb9db7f519136b9169352ff84af
diff --git a/requirements.txt b/requirements.txt
index 95ad247..108bbee 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,6 +4,6 @@
 
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 
-ddt>=1.0.1 # MIT
+ddt>=1.6.0 # MIT
 oslo.log>=3.36.0 # Apache-2.0
 tempest>=31.1.0 # Apache-2.0