Improve installation guide glance section
Improve installation guide glance section

I improved the glance verify section of the installation guide as
follows:

1) Clarified content.
2) Sourced admin-openrc.sh.

Change-Id: I8b2d346f715c37f680384a0ee3cbadf8fa184459
Implements: blueprint installation-guide-improvements

gongysh2004/openstack-manual,openstack/openstack-manuals,Akasurde/openstack-manuals,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,Akasurde/openstack-manuals,saeki-masaki/openstack-manuals,kairoaraujo/openstack-manuals,potsmaster/openstack-manuals,kairoaraujo/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,gongysh2004/openstack-manual,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,potsmaster/openstack-manuals