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

Conflicts:

	nova/tests/network/test_neutronv2.py

Change-Id: I45a24af11534911be68fd0964b79fdf726d88de6
(cherry picked from commit 10004672ad1476c55deaad53684a50358da6f656)
Merge "Remove unneeded call to conductor in network interface" into stable/havana