Updated openstack/openstack
Project: openstack/keystone  687eb6ff031915bb91cde75eb8ceed6799e8e1a0
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Make HACKING.rst DRYer

Reference the OpenStack hacking guide in HACKING.rst and remove
duplicated entries.

Change-Id: If82077e4f288b83b7d5d1ca68a2cc02d7644be4b