Migrate use of admin_token

[Luke Hinds]

`admin_token` is depreciated and recently removed from in paste-ini [1] with a recommendation is to move to using bootstrap. It will be removed entirely by keystone.

The current occurrences of admin_token are:

    $ grep -R AdminToken ./* | cut -d: -f1 | sort | uniq
    ./ceph-rgw.yaml
    ./keystone.yaml
    ./network/contrail-base.yaml
    ./neutron-midonet.yaml
    ./neutron-plugin-opencontrail.yaml

ceph/rgw have already proposed and merged a patch [2]

[1] https://review.openstack.org/#/c/427878/

[2] https://review.openstack.org/#/c/405625/

excerpt from keystone.conf

# Using this feature is *NOT* recommended. Instead, use the `keystone-manage
# bootstrap` command. The value of this option is treated as a "shared secret"
# that can be used to bootstrap Keystone through the API. This "token" does not
# represent a user (it has no identity), and carries no explicit authorization
# (it effectively bypasses most authorization checks). If set to `None`, the
# value is ignored and the `admin_token` middleware is effectively disabled.
# However, to completely disable `admin_token` in production (highly
# recommended, as it presents a security risk), remove
# `AdminTokenAuthMiddleware` (the `admin_token_auth` filter) from your paste
# application pipelines (for example, in `keystone-paste.ini`). (string value)

# This is deprecated in the M release and will be removed in the O release.
# Use `keystone-manage bootstrap` and remove this from the pipelines below.

[Emilien Macchi (emilienm)]

Excellent thing. I wanted to propose it for a while. Thanks!

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/493524

[OpenStack Infra (hudson-openstack)]

Change abandoned by Alex Schultz (<email address hidden>) on branch: master
Review: https://review.openstack.org/493524
Reason: Abandoning this patch per the TripleO Patch Abandonment guidelines (https://specs.openstack.org/openstack/tripleo-specs/specs/policy/patch-abandonment.html). If you wish to have this restored and cannot do so yourself, please reach out via #tripleo on freenode or the OpenStack Dev mailing list.

[Emilien Macchi (emilienm)]

This is an automated cleanup. This bug report has been closed because it
is older than 18 months and there is no open code change to fix this.
After this time it is unlikely that the circumstances which lead to
the observed issue can be reproduced.

If you can reproduce the bug, please:
* reopen the bug report (set to status "New")
* AND add the detailed steps to reproduce the issue (if applicable)
* AND leave a comment "CONFIRMED FOR: <RELEASE_NAME>"
  Only still supported release names are valid (FUTURE, PIKE, QUEENS, ROCKY, STEIN).
  Valid example: CONFIRMED FOR: FUTURE