Dedup HACKING.rst and remove any pep8 or OpenStack hacking rules

Point to OpenStack Style Guide instead of directly to pep8 (it points to
pep8). Remove any rules that are already covered in pep8 or in hacking.

This is the same format that integrated projects are using for there
hacking docs.

Change-Id: Idf35d3fafeb77428c9210b6c6a98eb8c319cc3de
Merge "Dedup HACKING.rst and remove any pep8 or OpenStack hacking rules"