create_params_lxc: storage parameter doesn't support size

The storage parameter is for the storage only, nothing more.
Use the rootfs parameter to correctly give the PVE API the disk size and the storage.

Addresses:
telcat#26 (comment)

lib/vagrant-proxmox/action/create_vm.rb

@@ -70,7 +70,7 @@ def create_params_lxc(config, env, vm_id)
 					 ostemplate: config.openvz_os_template,
 					 hostname: env[:machine].config.vm.hostname || env[:machine].name.to_s,
 					 password: 'vagrant',
-					 storage: "#{config.vm_storage}:#{config.vm_disk_size}",
+					 rootfs: "#{config.vm_storage}:#{config.vm_disk_size}",
 					 memory: config.vm_memory,
 					 description: "#{config.vm_name_prefix}#{env[:machine].name}"}
 					.tap do |params|