[user-guide]Update the content of log-in to the dashboard
[user-guide]Update the content of log-in to the dashboard

According to this commit 0e2337ec211f2ce009f594a16f458e4dc55cb144,
the mutil-domain credentials is set by default for Liberty. But the
End User Guide covers various release. Therefore, we need enter the
domain, user name and password, if the cloud enables the multi-domain
credentials.

Change-Id: Icb441717fc49b039c79eef608b6efa89de6e5c1b
Closes-Bug: #1554906

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