Move to common variant

This saves approximately 34kB in the compressed binary size of bmcweb
due to reduced template instantiations.  This amounts to a 2.5%
reduction in the overall size.

Note, there were a few places where we broke const-correctness in the
form of pulling a non-const reference out of a const variant.  This
new variant now requires const correctness, so some consts are
added where required.

Tested: Code compiles.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I6a60c8881c1268627eedb4ffddf16689dc5f6ed2
diff --git a/include/image_upload.hpp b/include/image_upload.hpp
index 1a0ace0..1b0a09a 100644
--- a/include/image_upload.hpp
+++ b/include/image_upload.hpp
@@ -5,6 +5,7 @@
 #include <boost/uuid/uuid_generators.hpp>
 #include <boost/uuid/uuid_io.hpp>
 #include <dbus_singleton.hpp>
+#include <dbus_utility.hpp>
 
 #include <cstdio>
 #include <fstream>
@@ -64,8 +65,8 @@
 
             sdbusplus::message::object_path path;
             std::vector<std::pair<
-                std::string,
-                std::vector<std::pair<std::string, std::variant<std::string>>>>>
+                std::string, std::vector<std::pair<
+                                 std::string, dbus::utility::DbusVariantType>>>>
                 interfaces;
             m.read(path, interfaces);