Make HACKING.rst DRYer
Make HACKING.rst DRYer

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

Change-Id: If82077e4f288b83b7d5d1ca68a2cc02d7644be4b

jonnary/keystone,klmitch/keystone,promptworks/keystone,dstanek/keystone,UTSA-ICS/keystone-kerberos,takeshineshiro/keystone,promptworks/keystone,rodrigods/keystone,promptworks/keystone,mahak/keystone,idjaw/keystone,jamielennox/keystone,vivekdhayaal/keystone,dims/keystone,reeshupatel/demo,reeshupatel/demo,UTSA-ICS/keystone-kerberos,rodrigods/keystone,jumpstarter-io/keystone,ilay09/keystone,openstack/keystone,cernops/keystone,dstanek/keystone,nuxeh/keystone,himanshu-setia/keystone,klmitch/keystone,cernops/keystone,takeshineshiro/keystone,mahak/keystone,openstack/keystone,dims/keystone,rajalokan/keystone,maestro-hybrid-cloud/keystone,himanshu-setia/keystone,derekchiang/keystone,JioCloud/keystone,dsiddharth/access-keys,jonnary/keystone,dstanek/keystone,MaheshIBM/keystone,mahak/keystone,blueboxgroup/keystone,reeshupatel/demo,ajayaa/keystone,rushiagr/keystone,rajalokan/keystone,roopali8/keystone,rushiagr/keystone,derekchiang/keystone,dsiddharth/access-keys,rushiagr/keystone,nuxeh/keystone,vivekdhayaal/keystone,idjaw/keystone,MaheshIBM/keystone,vivekdhayaal/keystone,jumpstarter-io/keystone,ilay09/keystone,JioCloud/keystone,dsiddharth/access-keys,ging/keystone,jumpstarter-io/keystone,ajayaa/keystone,openstack/keystone,derekchiang/keystone,maestro-hybrid-cloud/keystone,jamielennox/keystone,ilay09/keystone,nuxeh/keystone,roopali8/keystone,ging/keystone,rajalokan/keystone,blueboxgroup/keystone