Update link in HACKING.rst and Make it DRYer

* Fix URL for global hacking doc, related to
  I579e7c889f3addc2cd40bce0c584bbc70bf435e2
* Remove section on locals, as its already in openstack-dev/hacking
  (http://git.openstack.org/cgit/openstack-dev/hacking/tree/doc/source/index.rst#n154)

Change-Id: If944b088f343404c5b90b02afe6f781dd1db914d