[install] add a "node" and update the case of "dashboard"
[install] add a "node" and update the case of "dashboard"

This patch:

- adds the word "node" to improve the clarity of the sentence
- fixes the capitalization of horizon service name

Change-Id: Ie899c086e07ebdd9f35b089e28ffaf84be1774c8

openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals