tests: refactor common test infrastructure and fixtures

Change-Id: I597c11130eefa2cc2846ee6655c85dc04f2f22ef
diff --git a/tests/unit/security/validation-policy-accept-all.t.cpp b/tests/unit/security/validation-policy-accept-all.t.cpp
index 6a9f0f1..cd94cf7 100644
--- a/tests/unit/security/validation-policy-accept-all.t.cpp
+++ b/tests/unit/security/validation-policy-accept-all.t.cpp
@@ -40,7 +40,7 @@
 public:
   ValidationPolicyAcceptAllFixture()
   {
-    identity = addIdentity("/Security/TestValidationPolicyAcceptAll");
+    identity = m_keyChain.createIdentity("/Security/TestValidationPolicyAcceptAll");
     // don't add trust anchors
   }