The current instructions of "How to use with devstack" should be more
accurate and consistent with instructions of "Install Trove in DevStack"
page[1].

Adding a trove-dashboard plugin line to local.conf which is shown in "
Install Trove in DevStack" page[1] is not enough. Because you will see
the following error after executing "./stack.sh"::

    ++ /opt/stack/trove-dashboard/devstack/plugin.sh:source:34 :   configure_trove_dashboard
    ++ /opt/stack/trove-dashboard/devstack/plugin.sh:configure_trove_dashboard:10 :   cp -a /opt/stack/trove-dashboard/trove_dashboard/enabled/_1710_database_panel_group.py /opt/stack/trove-dashboard/trove_dashboard/enabled/_1720_project_databases_panel.py /opt/stack/trove-dashboard/trove_dashboard/enabled/_1730_project_database_backups_panel.py /opt/stack/trove-dashboard/trove_dashboard/enabled/_1731_project_database_backups_panel.py /opt/stack/trove-dashboard/trove_dashboard/enabled/_1740_project_database_clusters_panel.py /opt/stack/trove-dashboard/trove_dashboard/enabled/_1760_project_database_configurations_panel.py /opt/stack/trove-dashboard/trove_dashboard/enabled/__init__.py /opt/stack/horizon/openstack_dashboard/local/enabled/
    cp: target '/opt/stack/horizon/openstack_dashboard/local/enabled/' is not a directory
    + /opt/stack/trove-dashboard/devstack/plugin.sh:configure_trove_dashboard:1 :   exit_trap

I propose to add a full example of local.conf that includes trove
plugin and horizon service. Devstack is a tool to make an all-in-one
OpenStack environment for development. It is natural that trove and
trove-dashboard will be installed together. By doing so, developers
can easily make an all-in-one trove-dashboard environment.

1: https://docs.openstack.org/trove/latest/install/install-devstack.html



Story: 2007462
Task: 39142
Signed-off-by: Hirotaka Wakabayashi <hiwkby@yahoo.com>
Change-Id: Id05348b4ba7cf55f21297933ac60f5b7fcc2edbd