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_createhandler_unittest.cpp b/test/firmware_createhandler_unittest.cpp
index dc6d968..dd09cbe 100644
--- a/test/firmware_createhandler_unittest.cpp
+++ b/test/firmware_createhandler_unittest.cpp
@@ -31,7 +31,8 @@
     };
 
     auto handler = FirmwareBlobHandler::CreateFirmwareBlobHandler(
-        blobs, data, CreateTriggerMock(), CreateTriggerMock());
+        blobs, data, CreateTriggerMock(), CreateTriggerMock(),
+        CreateTriggerMock());
 
     //    EXPECT_EQ(handler, nullptr);
     EXPECT_FALSE(handler == nullptr);