travis: Use xvfb to run packer

This may help with SSH timeouts - apparently something is wrong when
Virtualbox starts without an X session, so the internal X session fails.

.travis.yml

@@ -8,8 +8,9 @@ before_install:
   usermod -aG vboxusers $(whoami)
 - mkdir output-virtualbox-iso && pushd output-virtualbox-iso && wget --progress=dot:giga https://github.com/sfalexrog/clever_vm/releases/download/v0.1_base_vm/clover-devel.ova
   && popd
+- sudo apt install -y xvfb
 script:
-- "./build.sh"
+- "xvfb-run ./build.sh"
 deploy:
   provider: s3
   access_key_id: XOJXX4IOM66XN7VZAFYX

ros_ide_vm.json

@@ -13,7 +13,7 @@
     "format": "ova",
     "guest_additions_mode": "disable",
 
-    "headless": "true",
+    "headless": "false",
 
     "vboxmanage": [
       ["modifyvm", "{{.Name}}", "--memory", "6144", "--vram", "128", "--mouse", "usbtablet", "--rtcuseutc", "on", "--nictype1", "virtio"],
@@ -73,4 +73,4 @@
     "source": "{{user `assetsDir`}}/vscode/",
     "destination": "/home/{{user `user`}}/.config/Code/User/"
   }]
-}
+}