tests: Implement IdentityManagementV2Fixture for v2::KeyChain

The old IdentityManagementFixture is renamed to IdentityManagementV1Fixture.

This commit also removes global KeyChainFixture, as it doesn't work with
TestKeyChain test suites.  Instead, IdentityManagementFixtures are
customizing PIB/TPM modules.

Change-Id: Iadc43b78523cd43bff4f454d6aea2fca8107a650
Refs: #2926
diff --git a/tests/unit-tests/util/io.t.cpp b/tests/unit-tests/util/io.t.cpp
index fcb1f2b..e4dfa63 100644
--- a/tests/unit-tests/util/io.t.cpp
+++ b/tests/unit-tests/util/io.t.cpp
@@ -269,7 +269,7 @@
 {
   Name identity("/TestIo/IdCert");
   identity.appendVersion();
-  BOOST_REQUIRE(addIdentity(identity, RsaKeyParams()));
+  addIdentity(identity, RsaKeyParams());
   Name certName = m_keyChain.getDefaultCertificateNameForIdentity(identity);
   shared_ptr<security::v1::IdentityCertificate> idCert;
   BOOST_REQUIRE_NO_THROW(idCert = m_keyChain.getCertificate(certName));