Changing DNS to pass string to driver

This commit also moves the "get_ip_address" functions out of
instance.views and into the models code under the SimpleInstance class,
where it's renamed get_visible_ip_addresses().
Also, the content field (the ip address) is now passed to the driver
instead of set on the Entry object by the manager, which allows more
flexibility for dealing with various drivers and will hopefully prevent
issues in the future.
Finally, integration tests were added to keep this from breaking
in the future.

Closes-Bug: 1273446

Change-Id: I70bf37838cc5cecfe579fe6001df79d7f6f5d53e
Merge "Changing DNS to pass string to driver"