feat(Vagrantfile): add fallback to rsync

In some cases (namely when using an encrypted filesystem),
a `vagrant up` will fail due to an NFS error. In these cases,
it is necessary to fall back to rsync to share code between the
local filesystem and the VM.

This commit adds a comment to the Vagrantfile with these instructions
and the necessary config directive.

related to #942

Author: carmstrong

Vagrantfile

@@ -44,11 +44,13 @@ Vagrant.configure("2") do |config|
 
       # Enable NFS for sharing the host machine into the coreos-vagrant VM.
       config.vm.synced_folder ".", "/home/core/share", id: "core", :nfs => true, :mount_options => ['nolock,vers=3,udp']
+      # FALLBACK use rsync if NFS has issues (mandatory if using Windows, or any Linux with an encrypted filesystem)
+      # config.vm.synced_folder ".", "/home/core/share", type: "rsync"
+      # Note that with rsync, local Deis code changes need to be re-synced to the VM by issuing a `vagrant reload --provision`
 
       # user-data bootstrapping
       config.vm.provision :file, :source => "contrib/coreos/user-data", :destination => "/tmp/vagrantfile-user-data"
       config.vm.provision :shell, :inline => "mv /tmp/vagrantfile-user-data /var/lib/coreos-vagrant/", :privileged => true
-
     end
   end