Fix whitespace for interfaces file with two interfaces and IPv6

[Rick Harris]

If you have more than one interface and IPv6 is enabled, then the interfaces file will be broken: the 'auto` line will be on the same line as the previous stanza's gateway:

auto eth0
iface eth0 inet static
    address 192.168.0.2
    netmask 255.255.255.0
    gateway 192.168.0.1 auto eth1
iface eth1 inet static
    ...

vs

auto eth0
iface eth0 inet static
    address 192.168.0.2
    netmask 255.255.255.0
    gateway 192.168.0.1
auto eth1
iface eth1 inet static
    ...

The solution is fix the Jinja whitespace control in the template.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/105881

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/105881
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=383d0c945e4874d7e66ad8ed03fe6556ac7c03d8
Submitter: Jenkins
Branch: master

commit 383d0c945e4874d7e66ad8ed03fe6556ac7c03d8
Author: Rick Harris <email address hidden>
Date: Tue May 27 16:09:40 2014 -0500

    Fix interfaces template for two interfaces and IPv6

    If you have more than one interface and IPv6 enabled, then the interfaces file
    emitted would have the incorrect syntax: the `auto eth1` line would be
    appended to the end of the `gateway` line of the previous stanza.

    This was a result of improper whitespace control in the Jinja template which
    this patch fixes.

    In order to prevent regressions, this patch swaps out the existing tests with
    corresponding tests that are whitespace sensitive. This is important because
    it's difficult to tweak Jinja templates in a way that fixes the whitespace
    for one scenario while not breaking another.

    Closes-Bug: 1339888

    Change-Id: Id5566ea2f93ee1a6b8bc42e83bc64a1c6a09e680