tests: IdentityManagementFixture no longer derives from BaseFixture

Also rename it to KeyChainFixture

Refs: #4528
Change-Id: Id86f4affc9c4c9ae159912430cc3e78557bf1ac2
diff --git a/tests/daemon/rib/readvertise/host-to-gateway-readvertise-policy.t.cpp b/tests/daemon/rib/readvertise/host-to-gateway-readvertise-policy.t.cpp
index c455065..aaff73e 100644
--- a/tests/daemon/rib/readvertise/host-to-gateway-readvertise-policy.t.cpp
+++ b/tests/daemon/rib/readvertise/host-to-gateway-readvertise-policy.t.cpp
@@ -25,7 +25,7 @@
 
 #include "rib/readvertise/host-to-gateway-readvertise-policy.hpp"
 
-#include "tests/identity-management-fixture.hpp"
+#include "tests/key-chain-fixture.hpp"
 
 #include <ndn-cxx/security/signing-helpers.hpp>
 
@@ -35,7 +35,7 @@
 
 using namespace nfd::tests;
 
-class HostToGatewayReadvertisePolicyFixture : public IdentityManagementFixture
+class HostToGatewayReadvertisePolicyFixture : public BaseFixture, public KeyChainFixture
 {
 public:
   static RibRouteRef