Switch integration tests to Ubuntu 14.04

refs #3067

Change-Id: I343deb71b500cf90e5ae905893584f6f275a4117
diff --git a/Vagrantfile b/Vagrantfile
index 3edc96b..0177d66 100644
--- a/Vagrantfile
+++ b/Vagrantfile
@@ -49,7 +49,7 @@
 SCRIPT
 
 Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
-  config.vm.box = "ubuntu/precise64"
+  config.vm.box = "ubuntu/trusty64"
 
   config.vm.provider "virtualbox" do |vb|
     vb.memory = "4096"