bmc: move verify systemd mode to parameter

Move the mode for the trigger service to a parameter instead of
hard-coding it.  This isn't yet a json configuration option, that'll be
next.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I59564320015c22be1ec3a4701479d0ee93b9f1f7
diff --git a/bmc/test/firmware_json_unittest.cpp b/bmc/test/firmware_json_unittest.cpp
index 04c0f09..8b4f130 100644
--- a/bmc/test/firmware_json_unittest.cpp
+++ b/bmc/test/firmware_json_unittest.cpp
@@ -1,5 +1,6 @@
 #include "buildjson.hpp"
 #include "update_systemd.hpp"
+#include "verify_systemd.hpp"
 
 #include <nlohmann/json.hpp>
 
@@ -423,6 +424,9 @@
     EXPECT_FALSE(h[0].actions == nullptr);
     EXPECT_FALSE(h[0].actions->preparation == nullptr);
     EXPECT_FALSE(h[0].actions->verification == nullptr);
+    auto verifier = reinterpret_cast<SystemdVerification*>(
+        h[0].actions->verification.get());
+    EXPECT_THAT(verifier->getMode(), "replace");
     EXPECT_FALSE(h[0].actions->update == nullptr);
     auto updater =
         reinterpret_cast<SystemdUpdateMechanism*>(h[0].actions->update.get());