Add security group failed with NotFound error

[hongbin]

Description
===========
On processing the request to add a security group to a container, it failed with a NotFound error on performing a neutron API call:

  http://paste.openstack.org/show/643335/

This bug was introduced by: https://review.openstack.org/#/c/531561/ . That patch has a side effect that makes the context elevation ineffective. As a result, the neutron API call was made by a non-admin context thus failing to add the security group to the port.

Reproduce
=========
#### create container in demo tenant ####
$ source /opt/stack/devstack/openrc demo demo
$ openstack appcontainer run --name test nginx
$ CONTAINER_PORT=1709b046-44ae-4e89-b399-81f4c84221f4

#### populate neutron port in admin tenant ####
$ source /opt/stack/devstack/openrc admin admin
$ openstack security group create adminsg
$ openstack port set --security-group adminsg $CONTAINER_PORT

#### add security group in demo tenant ####
$ source /opt/stack/devstack/openrc demo demo
$ openstack security group create demosg
$ openstack appcontainer add security group test demosg

# check the log of devstack@zun-compute, it should fail

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/532962
Committed: https://git.openstack.org/cgit/openstack/zun/commit/?id=abd7e2b08f05383fb05c66f7bc57ffb7f7a2ab9e
Submitter: Zuul
Branch: master

commit abd7e2b08f05383fb05c66f7bc57ffb7f7a2ab9e
Author: Hongbin Lu <email address hidden>
Date: Thu Jan 11 20:09:29 2018 +0000

    Fix an issue on context elevation

    The issue was introduced by:
    https://review.openstack.org/#/c/531561/
    That patch above fixed an issue of creating volumes in a wrong
    tenant, but it made the context elevation ineffective. As a result,
    some neutron API calls (i.e. port update) was made by a non-admin
    context thus failing due to insufficient permission.

    This patch fixed it by using get_admin_context instead of
    context.elevated().

    Closes-Bug: #1742840
    Change-Id: Ia68729b90d059d7d88a00915582453d38420ab24

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/zun 1.0.0 release.