Deprecate use_namespaces option

[Assaf Muller]

use_namespaces was introduced because at the time not all kernels properly supported namespaces. That time has passed, and since:

1) The non-default (False) value is not being tested
2) It has introduced complexity in the L3 and DHCP agents

More information may be found here:
http://lists.openstack.org/pipermail/openstack-dev/2015-March/059519.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/166888

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/166888
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=9902c101f26c72bd416e07c4539a4d63945a86c7
Submitter: Jenkins
Branch: master

commit 9902c101f26c72bd416e07c4539a4d63945a86c7
Author: Assaf Muller <email address hidden>
Date: Mon Mar 23 11:27:00 2015 -0400

    Deprecate use_namespaces option

    Change-Id: I3a769a0195aba45ec836b669fe049f0b8eba884f
    Closes-Bug: #1435382

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/238213

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/238213
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=23b907bc6e87be153c13b1bf3e069467cdda0d27
Submitter: Jenkins
Branch: master

commit 23b907bc6e87be153c13b1bf3e069467cdda0d27
Author: Cedric Brandily <email address hidden>
Date: Wed Oct 21 20:52:40 2015 +0200

    Remove deprecated use_namespaces option

    The use_namespaces option has been defined as a workaround to kernels
    not properly supporting namespaces. This limitation is behind us, it's
    time to remove use_namespaces after its deprecation in Kilo in order to
    simplify code and remove a poorly tested case (use_namespaces=False).

    This change prepares for removal pullup_route method[1] which was only
    used when use_namespaces=False.

    [1] neutron.agent.linux.ip_lib

    DocImpact
    UpgradeImpact
    Closes-Bug: #1508188
    Related-Bug: #1435382
    Depends-On: I303038eec560a6d99421140c2822aed8b518470b
    Depends-On: I4feb2a15c7e1e4bfdbed2531b18b8e7d798ab3cc
    Change-Id: I2fbf65df1250d9f9f1656b3964ee3b6de1ef1118

[OpenStack Infra (hudson-openstack)]

Change abandoned by Darek Smigiel (<email address hidden>) on branch: master
Review: https://review.openstack.org/295901
Reason: garyk's patch here: https://review.openstack.org/#/c/296354/