Vagrantfile: Add workaround for Virtualbox bug on guest audio config

Seems like Virtualbox is having troubles adding audio to guests[1].
Since we don't care about audio, we can simply disable that in order
to workaround this problem:

/usr/share/vagrant/plugins/providers/virtualbox/driver/version_5_0.rb:670:in
`start': There was an error while executing `VBoxManage`, a CLI used by
Vagrant (Vagrant::Errors ::VBoxManageError)
for controlling VirtualBox. The command and stderr is shown below.

Command: ["startvm", "145b5aec-b9c5-4feb-9728-e8670bb71b48", "--type",
"headless"]

Stderr: VBoxManage: error: The specified string / bytes buffer was to
small. Specify a larger one and retry. (VERR_CFGM_NOT_ENOUGH_SPACE)
VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005),
component ConsoleWrap, interface IConsole
There was an error while executing `VBoxManage`, a CLI used by Vagrant
for controlling VirtualBox. The command and stderr is shown below.

Command: ["startvm", "145b5aec-b9c5-4feb-9728-e8670bb71b48", "--type",
"headless"]

Stderr: VBoxManage: error: The specified string / bytes buffer was to
small. Specify a larger one and retry. (VERR_CFGM_NOT_ENOUGH_SPACE)
VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005),
component ConsoleWrap, interface IConsole

[1] https://github.com/hashicorp/vagrant/issues/9524

Change-Id: Id10cd882b08d9ca9ec661c280d8549fa13af6243

Vagrantfile

@@ -18,6 +18,8 @@ Vagrant.configure(2) do |config|
   config.vm.provider "virtualbox" do |v|
     v.memory = 6144
     v.cpus = 2
+    # https://github.com/hashicorp/vagrant/issues/9524
+    v.customize ["modifyvm", :id, "--audio", "none"]
   end
 
   config.vm.synced_folder ".", "/vagrant", type: "rsync"