Use openstack.org git infrastructure for samples.

Updated guides to use the openstack.org git infrastructure for
retrieving sample files from the various OpenStack projects. This
prevents sporadic github outages breaking the guide builds.

Change-Id: Ic637899d2bfa4da1d64b26ef35792d9607458c51
Nova quota content is shared.

Nova quota content is shared between the configuration reference and the
admin user guide. The content has been moved to common and files that
point to it updated.

Change-Id: Iad80f281eb025aa93c773f3eb858e27afb9d0bdc
Merge "Nova quota content is shared."
Merge "Use openstack.org git infrastructure for samples."