Add IPAddress field type in object models

In object models, there are ipv4 address type and ipv6 address type.
However, for some fields in models.py, for instance, host_ip in compute node,
and a bunch of IPAddress variables in network, and address in other tables.

There is no field type corresponding to them, no matter whether it is v4 or
v6. So, add one more field type in object models to specify that type.

Change-Id: Ic53ed644f4bbc1e280b2f8cbb9b9c145c3d8a2e9
Remove unneeded call to conductor in network interface

The following patch removes an unneeded call to conductor to retrieve
data already available in instance.

Note: six.text_type() was added and wrapped around info_cache in some of
the tests. This was done because values from the db are in unicode
(text_type). The reason the test changed is because previously we
did not check the type of string from what the conductor was returning.

Closes-bug: #1258360

Change-Id: I45a24af11534911be68fd0964b79fdf726d88de6
Merge "Add IPAddress field type in object models"
Merge "Remove unneeded call to conductor in network interface"