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/buildjson.cpp b/bmc/buildjson.cpp
index d8a9ea1..60575db 100644
--- a/bmc/buildjson.cpp
+++ b/bmc/buildjson.cpp
@@ -91,8 +91,9 @@
             {
                 const auto& path = verify.at("path");
                 const auto& unit = verify.at("unit");
+                const std::string mode = "replace";
                 pack->verification = SystemdVerification::CreateVerification(
-                    sdbusplus::bus::new_default(), path, unit);
+                    sdbusplus::bus::new_default(), path, unit, mode);
             }
             else
             {