Add Vagrantfile

This patch allows us to develop and test couchdb using vagrant
(http://www.vagrantup.com) .

Since we don't have any good debian packaging for now this image is only
useful for developers or those who want to use latest couchdb version.

To use it run the following commad:

    $ vagrant up
    $ vagrant ssh
    $ cd /vagrant

then you can play with the code and build your own distribution of
couch. This image is supporting lxc, ec2 and rackspace providers for
vagrant.