vagrant: Switch to c7alpha, set up sshfs

The default C7 box gets old, I'd like to have Alpha be a focus
for development.

Let's use sshfs if available.

Closes: #516
Approved by: jlebon

Vagrantfile

@@ -7,7 +7,8 @@ Vagrant.configure(2) do |config|
     if ENV['VAGRANT_BOX']
       config.vm.box = ENV['VAGRANT_BOX']
     else
-      config.vm.box = "centos/atomic-host"
+      config.vm.box = "centosah/7alpha"
+      config.vm.box_url = 'https://ci.centos.org/artifacts/sig-atomic/centos-continuous/images-alpha/cloud/latest/images/centos-atomic-host-7-vagrant-libvirt.box'
     end
 
     config.vm.hostname = "centosah-dev"
@@ -15,6 +16,9 @@ Vagrant.configure(2) do |config|
     config.vm.define "vmcheck" do |vmcheck|
     end
 
+    if Vagrant.has_plugin?('vagrant-sshfs')
+      config.vm.synced_folder ".", "/var/home/vagrant/sync", type: 'sshfs'
+    end
     # turn off the default rsync in the vagrant box (the vm tooling does this
     # for use already)
     config.vm.synced_folder ".", "/home/vagrant/sync", disabled: true