Support "split horizon" DNS

This is a set of patches to implement "split-horizon" DNS in Eucalyptus.  Currently, it requires that each instance be provided with two DNS servers -- the first being the CLC's DNS service, for internal lookups, and the second being a DNS server capable of recursive lookups.  It's perhaps not the ideal solution, but was sufficient for my testing, and it does not substantially change the architecture of the services.

I'd like to carry this patch in Fedora, since Eucalyptus's DNS behavior without it is fundamentally different from AWS, and I would like to provide users a more similar experience.