Should add `trove` installation in devstack's local conf

[Eric Xie]

Description
===========
In the latest git version, trove already is added in karbor's protectables.
But in the devstack/local.conf.sample, the installation for trove was not added.

Steps to reproduce
==================
* Clone latest devstack
* Use devstack/local.conf.sample as local.conf in env
* Execute ./stack.sh

Expected result
===============
Trove should be installed

Actual result
=============
Trove was not installed

Environment
===========
1. devstack version
$ git log
commit 614cab33c40159f0bc10d92c9f8dc3f9783708d9
Merge: b5841fa 0b45e2f
Author: Zuul <email address hidden>
Date: Sun Jan 21 22:08:24 2018 +0000

    Merge "Remove hack for ubuntu cloud archive"

2. karbor-dashboard version
$ git log
commit 761570ef879603188e546bc324ea883228c31114
Author: OpenStack Proposal Bot <email address hidden>
Date: Wed Dec 13 07:08:52 2017 +0000

    Imported Translations from Zanata

    For more information about this automatic import see:
    https://docs.openstack.org/i18n/latest/reviewing-translation-import.html

    Change-Id: I51824947b49b97d592e080d66efea4538a248aa9

Logs
==============
Jan 23 10:36:40 localhost karbor-protection: 2018-01-23 10:36:40.947 3995 ERROR karbor.services.protection.protectable_plugins.database [req-3cbff002-3fbd-4fa4-a804-2b53eee44152 a2ec3577595c4003824f0ad06744eb8a 9d0bfb331dcd4d67a9cef16a290b760e - - -] List all database instances from trove failed.: KarborException: Couldn't find the endpoint of service(trove)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/536661

[OpenStack Infra (hudson-openstack)]

Change abandoned by Eric Xie ([e-mail]) on branch: master
Review: https://review.openstack.org/536661