bmc: add preparation step before data is received

Add a preparation systemd trigger event before data is received.  On
systems under memory pressure, this'll trigger a service that can do
things like flush caches.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I175177f4a91b58d9f163098572a9d2614002b718
diff --git a/test/firmware_state_notyetstarted_tarball_unittest.cpp b/test/firmware_state_notyetstarted_tarball_unittest.cpp
index 5aa2baa..275763c 100644
--- a/test/firmware_state_notyetstarted_tarball_unittest.cpp
+++ b/test/firmware_state_notyetstarted_tarball_unittest.cpp
@@ -36,7 +36,8 @@
         updateMockPtr = reinterpret_cast<TriggerMock*>(updateMock.get());
 
         handler = FirmwareBlobHandler::CreateFirmwareBlobHandler(
-            blobs, data, std::move(verifyMock), std::move(updateMock));
+            blobs, data, CreateTriggerMock(), std::move(verifyMock),
+            std::move(updateMock));
     }
 
     void expectedState(FirmwareBlobHandler::UpdateState state)