config_dashboard does not disable dashboard properly

[Georg Hoesch]

Note: I will explain the bug with the 'octavia' dashboard, but it should apply to dashboards in general.

How to reproduce
- kolla, branch 'victoria' (but also in master)
- deploy with 'enable_octavia: "no"' (this is the default)
- open horizon GUI with a user (anyone)
- browse to 'Project - Network'
- You will see a menu item 'Load Balancers' that shouldn't be there.
  The page works, but only yields errors (because the services doesn't exist).

Bug analysis:
- the horizon container is started with environment variables for enabling/disabling plugins
  (this works)
- horizons extend_start.sh has a function config_dashboard() that checks these variables
  and does the job
- config-dashboard() does either create or remove
  /usr/lib/python3/dist-packages/openstack_dashboard/local/enabled/_1482_project_load_balancer_panel.py
  mind the 'local/enabled' in the path!
- the very same file is also present in
  'enabled/_1482_project_load_balancer_panel.py'
- The latter is loaded if no local settings overrides it, so the dashboard is always enabled

Solution:
- according to the docs, 'local/enabled' is only for local extra configuration
  (see https://docs.openstack.org/horizon/latest/configuration/pluggable_panels.html)
- kolla should use the 'enabled' directory instead of 'local/enabled'
- if kolla really has special local files, both directories have to be provisioned