This exports Rackspace DNS domains to bind format for backup and
migration purposes.
This installs a small tool to query and export all the domains we can
see via the Racksapce DNS API.
Because we don't want to publish the backups (it's the equivalent of a
zone xfer) it is run on, and logs output to, bridge.openstack.org from
cron once a day.
Change-Id: I50fd33f5f3d6440a8f20d6fec63507cb883f2d56
ccd3ac2344