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_commit_unittest.cpp b/test/firmware_commit_unittest.cpp
index 11ce3fc..b8c651e 100644
--- a/test/firmware_commit_unittest.cpp
+++ b/test/firmware_commit_unittest.cpp
@@ -49,7 +49,8 @@
         std::make_unique<StrictMock<TriggerMock>>();
 
     auto handler = FirmwareBlobHandler::CreateFirmwareBlobHandler(
-        blobs, data, std::move(verifyMock), CreateTriggerMock());
+        blobs, data, CreateTriggerMock(), std::move(verifyMock),
+        CreateTriggerMock());
 
     EXPECT_CALL(imageMock2, open("asdf")).WillOnce(Return(true));
 
@@ -71,7 +72,8 @@
         std::make_unique<StrictMock<TriggerMock>>();
 
     auto handler = FirmwareBlobHandler::CreateFirmwareBlobHandler(
-        blobs, data, std::move(verifyMock), CreateTriggerMock());
+        blobs, data, CreateTriggerMock(), std::move(verifyMock),
+        CreateTriggerMock());
 
     EXPECT_CALL(imageMock1, open(StrEq(hashBlobId))).WillOnce(Return(true));