CLI: Implement unlinking, DNS servers for dhcp, and other fixes.

Fixes MN-191, MN-192.

Also addresses the following issues:
-The -A flag now actually skips authentication.
-The set operation now supports object references.
-Support sending empty lists in API calls.

Signed-off-by: Brandon Berg <bberg@midokura.jp>
Merge pull request #54 from brandon-berg/master

CLI: Implement unlinking, DNS servers for dhcp, and other fixes.