Adding feature to define domain_specific_drivers

The patch make a possibility to define domain_specific_drivers parameter in
section [identity-feature-enabled] for tempest in case of external domain
is used in keystone.

Change-Id: Iaf7a8f8aee7afb82ee4fb74d1934acc8fe861de2
Related-PROD: PROD-26288 (PROD:26288)
diff --git a/_modules/runtest/tempest_sections/identity_feature_enabled.py b/_modules/runtest/tempest_sections/identity_feature_enabled.py
index 166bebd..e3fd4e2 100644
--- a/_modules/runtest/tempest_sections/identity_feature_enabled.py
+++ b/_modules/runtest/tempest_sections/identity_feature_enabled.py
@@ -1,6 +1,8 @@
 
 import base_section
 
+from runtest import conditions
+
 class IdentityFeatureEnabled(base_section.BaseSection):
 
     name = "identity-feature-enabled"
@@ -34,7 +36,10 @@
 
     @property
     def domain_specific_drivers(self):
-        pass
+        c = conditions.BaseRule('keystone.server.enabled', 'eq', True)
+        keystone_domain = self.get_item_when_condition_match('keystone.server.domain', c)
+        if keystone_domain:
+           return True
 
     @property
     def forbid_global_implied_dsr(self):