Set safe version of hacking

Versions of hacking from 3.1.0 until 4.0.0 NOT included are supposed
to require a safe version of flake8, so besides normale issues related
to minor version upgrades, we can safely use those versions.
Also forcing pycodestyle versions to be compatible with flake8 installed
by hacking.

Change-Id: Idb66f2ae0105308747cdf3046b09a22bdf691ea3
1 file changed