Separate static assignments per zone for same MAC

[emmaly]

Right now the static IP assignments (and non-static as well) are recorded in etcd as /dhcp/$MAC/ip. That doesn't allow for a different value per zone. We need to be able to do something like /dhcp/$MAC/$ZONE/ip or something like it.

For example, we will definitely have laptops going from one office to another. We won't always want/need them to be static assignments, but when we do, we will fail until we fix this.

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Note: This issue was migrated from https://bitbucket.org/dustywilson/netcore/issues/1 originally created on 2015-01-30 by Dusty Wilson. It was not evaluated in any way for freshness and validity.