Use move semantics in cmd line parsing

hcore/deviceManager/deviceSpecParser.cpp

@@ -21,7 +21,7 @@ std::string DeviceManager::readDeviceFile(const std::string& filename)
         (std::istreambuf_iterator<char>(file)),
         std::istreambuf_iterator<char>());
 
-    return content;
+    return std::move(content);
 }
 
 void DeviceManager::collateAllDeviceSpecs(const OptionParser& options)