KVM: selftests: Print expected and actual exit reason in KVM exit reason assert

Print what KVM exit reason a test was expecting and what it actually
got int TEST_ASSERT_KVM_EXIT_REASON().

Signed-off-by: Vipin Sharma <vipinsh@google.com>
Message-Id: <20230204014547.583711-3-vipinsh@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>