add admin credentials in swift install guide for ubuntu
add admin credentials in swift install guide for ubuntu

add "source admin-openrc.sh" before create swift user.
already checked by apache maven in local environment.

URL: http://docs.openstack.org/kilo/install-guide/install/apt/content/swift-install-controller-node.html
Change-Id: I7a830ecf68f385912c04e31ce749ee143b38112c
Closes-Bug: #1473312

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