Cleanup and make HACKING.rst DRYer

Reference the OpenStack hacking guide in HACKING.rst and remove
duplicate entries. Adds placeholder section for neutron specific
rules.

Change-Id: I4bfbab50b77e7592178dda44c7f4f52edc7fdc21
Merge "Cleanup and make HACKING.rst DRYer"
Imported Translations from Transifex

Change-Id: Ide68c511286feddf695153369c8bed007c528932