List namespaces properly, fix regression introduced by fix to 1293818

[Eugene Nikanorov]

fix to 1293818 introduced a regression for the code path that is used in loadbalancer namespace driver to list namespaces.
The following tracebacks are seen during tempest runs:

http://logs.openstack.org/14/82514/2/check/check-tempest-dsvm-neutron-pg/73ff42d/logs/screen-q-lbaas.txt.gz?level=TRACE#_2014-03-25_09_49_57_261

As a consequence, this causes agent to resync balancer state and to respawn haproxy process sometimes leading to unavailable service. That in turn makes loadbalancer basic scenario test fail.

Related bugs: 1294603, 1295165

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/81537
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=14b6611efea4c9658c611e8cfcfb42fc7dd82f55
Submitter: Jenkins
Branch: master

commit 14b6611efea4c9658c611e8cfcfb42fc7dd82f55
Author: Eugene Nikanorov <email address hidden>
Date: Wed Mar 19 18:00:35 2014 +0400

    Fix namespace exist() method

    Fix namespace exist() method for it shall not be called with a root.
    Also, don't run it under the namespace so garbage_collect_namespace
    method can run without rootwrap and not withi a ns.

    As a result of fixing namespace listing the patch also fixes the
    regression introduced (bug/1294603) to loadbalancer agent respawning
    haproxy due to inability to list namespaces properly.

    Change-Id: I0dc4d01b0c1c04887ec6ad5766ec7c6c96903faa
    Closes-Bug: #1297594
    Closes-Bug: #1294603