Changed Vagrantfile settings

Adjusted the vagrant settings to try to improve the building
performance:

* Moved from ubuntu/xenial64 to ubuntu/artful64
* 4096M memory
* 4 CPUs

Vagrantfile

@@ -2,10 +2,11 @@
 # vi: set ft=ruby :
 
 Vagrant.configure("2") do |config|
-  config.vm.box = "ubuntu/xenial64"
+  config.vm.box = "ubuntu/artful64"
 
   config.vm.provider "virtualbox" do |vb|
-    vb.memory = "1024"
+    vb.memory = "4096"
+    vb.cpus = 4
   end
 
   config.vm.provision "shell", inline: <<-SHELL
@@ -20,5 +21,6 @@ Vagrant.configure("2") do |config|
     pip3 install docker-compose
     systemctl daemon-reload
     systemctl restart docker
+    apt install -y qemu
   SHELL
 end