The admin config resize doc was linking to a now non-existent
user guide doc which was deleted in pike. This change imports
the resize user guide from the openstack-manuals stable/ocata
branch, fixes the link, and updates the resize user doc to
(1) link to our internal shutdown_timeout config option reference
and (2) link to the image properties doc in glance for the
os_shutdown_timeout image property.
Change-Id: I9988abfd344d1d3b0b6eaf32b036369b51853965
Closes-Bug: #1784715
3cd5198d5a