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/chassis_state_manager.cpp b/chassis_state_manager.cpp
index 0215535..9e298e9 100644
--- a/chassis_state_manager.cpp
+++ b/chassis_state_manager.cpp
@@ -270,8 +270,7 @@
                 using Property = std::string;
                 using Value = std::variant<bool, uint>;
                 using PropertyMap = std::map<Property, Value>;
-                PropertyMap properties;
-                response.read(properties);
+                auto properties = response.unpack<PropertyMap>();
 
                 if (std::get<uint>(properties["Type"]) != TYPE_UPS)
                 {
@@ -374,8 +373,7 @@
                 using Property = std::string;
                 using Value = std::variant<std::string>;
                 using PropertyMap = std::map<Property, Value>;
-                PropertyMap properties;
-                response.read(properties);
+                auto properties = response.unpack<PropertyMap>();
 
                 auto statusStr = std::get<std::string>(properties["Status"]);
                 auto status =
diff --git a/host_check.cpp b/host_check.cpp
index bc1ade1..436bd92 100644
--- a/host_check.cpp
+++ b/host_check.cpp
@@ -98,8 +98,9 @@
                     HostFirmware::property_names::current_firmware_condition);
 
                 auto response = bus.call(method);
-                std::variant<HostFirmware::FirmwareCondition> currentFwCondV;
-                response.read(currentFwCondV);
+                auto currentFwCondV = response.unpack<
+                    std::variant<HostFirmware::FirmwareCondition>>();
+
                 auto currentFwCond =
                     std::get<HostFirmware::FirmwareCondition>(currentFwCondV);
 
@@ -141,8 +142,8 @@
                       Chassis::property_names::current_power_state);
 
         auto response = bus.call(method);
-        std::variant<Chassis::PowerState> currentPowerStateV;
-        response.read(currentPowerStateV);
+        auto currentPowerStateV =
+            response.unpack<std::variant<Chassis::PowerState>>();
 
         auto currentPowerState =
             std::get<Chassis::PowerState>(currentPowerStateV);
diff --git a/host_reset_recovery.cpp b/host_reset_recovery.cpp
index 6faf77e..7eff420 100644
--- a/host_reset_recovery.cpp
+++ b/host_reset_recovery.cpp
@@ -52,8 +52,8 @@
 
         auto response = bus.call(method);
 
-        std::variant<ProgressStages> bootProgressV;
-        response.read(bootProgressV);
+        auto bootProgressV = response.unpack<std::variant<ProgressStages>>();
+
         auto bootProgress = std::get<ProgressStages>(bootProgressV);
 
         if (bootProgress == ProgressStages::Unspecified)
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)