Release 0.3.0

Backwards-incompatible changes

• Nodes have now an id field, matching the VirtualBox UUID.
  You must recreate all the nodes defined in your ~/.libcloud-vagrant
  catalogue.

Backwards-compatible changes

• New command-line tool libcloud-vagrant to do simple operations
  with Vagrant nodes created by Libcloud.
• Interactions with Vagrant and Virtualbox are protected by a
  filesystem-based lock.
• Unit tests use now a free 24-bit network in the 192.168/16 range,
  instead of using hard-coded ones.
• The host network interfaces of public networks are destroyed when the
  Vagrant network objects are destroyed.
• libcloud-vagrant now makes fewer calls to the Virtualbox
  VBoxManage command.