Add vnc_server_header parameter

Change-Id: Ib07a8b6016ea645309b44f558c67c00447e794e6
Related-Issue: PROD-20509
diff --git a/_modules/runtest/tempest_sections/compute_feature_enabled.py b/_modules/runtest/tempest_sections/compute_feature_enabled.py
index 91eb882..d2b3f9a 100644
--- a/_modules/runtest/tempest_sections/compute_feature_enabled.py
+++ b/_modules/runtest/tempest_sections/compute_feature_enabled.py
@@ -35,6 +35,7 @@
         'suspend',
         'swap_volume',
         'vnc_console',
+        'vnc_server_header',
     ]
 
 
@@ -184,3 +185,7 @@
         #TODO: fix when value is unhardcoded.
         return conditions.BaseRule('*.nova.compute.enabled', 'eq', True,
                             multiple='any').check(self.pillar)
+
+    @property
+    def vnc_server_header(self):
+        return 'nginx'