use sdbusplus unpack syntax

Rather than defining a variable and then reading it from a message,
sdbusplus also supports directly unpack-ing from the message.  Use
this syntax instead as it is more efficient and succinct.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I5ff2aa545ba88d06ea6ac95b83a329c7dfe8594e
diff --git a/host_state_manager.cpp b/host_state_manager.cpp
index 7637816..59b900f 100644
--- a/host_state_manager.cpp
+++ b/host_state_manager.cpp
@@ -219,8 +219,8 @@
     try
     {
         auto reply = bus.call(methodOneTime);
-        std::variant<bool> result;
-        reply.read(result);
+        auto result = reply.unpack<std::variant<bool>>();
+
         auto autoReboot = std::get<bool>(result);
 
         if (!autoReboot)