Initial Vagrant configurations

Add two vagrant configurations.

* rackspace-convert-base - used for taking a Rackspace base image and
  prepping it for use with other Vagrant definitions

* ovsdb-devstack - the current definition used for the OVSDB projects'
  DevStack testing dynamic slave. Please note that while this was used
  in the creation of the image used by OVSDB it was not the final
  vagrant. The Linux Foundation has an additional overlay that it uses
  to configure networking needs for the Rackspace private network that
  they operating the build environment inside of. As this extra overlay
  includes private configuration data it is not being added to the
  repository.

Change-Id: I800a096042ef196efceae6f2f19db754728415ee
Signed-off-by: Andrew Grimberg <agrimberg@linuxfoundation.org>