Prime hostname cache during initial configuration

Author: kattrali

src/main/java/com/bugsnag/Configuration.java

@@ -34,6 +34,7 @@ public class Configuration {
         // Add built-in callbacks
         addCallback(new AppCallback(this));
         addCallback(new DeviceCallback());
+        DeviceCallback.initializeCache();
 
         if (ServletCallback.isAvailable()) {
             addCallback(new ServletCallback());

src/main/java/com/bugsnag/callbacks/DeviceCallback.java

@@ -35,6 +35,10 @@ public String get() {
             }
         });
 
+    public static void initializeCache() {
+        hostnameCache.get();
+    }
+
     @Override
     public void beforeNotify(Report report) {
         report