Comment 2 for bug 1790864

Reviewed: https://review.openstack.org/615425
Committed: https://git.openstack.org/cgit/openstack/tempest/commit/?id=3588bb3f5ef546a0ef4d4ad621fd1be381b5fdaf
Submitter: Zuul
Branch: master

commit 3588bb3f5ef546a0ef4d4ad621fd1be381b5fdaf
Author: Attila Fazekas <email address hidden>
Date: Sun Nov 4 12:40:27 2018 +0100

    interfaces_by_fixed_ip no extra port

    test_create_list_show_delete_interfaces_by_fixed_ip was allowed
    to make one extra port/interface creation optional
    in case the CONF.compute.fixed_network_name was defined,
    but in this case the test failed at teardown time (double port delete).
    Turned out the test case normally not even deletes the fixed_ip port,
    inside the test case.

    There is no point for having 3 interface in this test, so just
    adding/deleting the fixed_ip interface
    and removing th 3th `extra` interface part from the test.

    The extra port was problematic in (multiple) shared network case,
    however fixed_ip interface creation part
    has the right logic to use an explicit network.

    Related-Bug: #1790864
    Change-Id: I6e3e53c4ac26b4fef09fefb9c590dfa91f577565