The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.
Fix problems found.
Update local hacking checks for new flake8.
Remove hacking and friends from lower-constraints, those are not needed
for co-installing.
Change-Id: I926efaef501f190e78da9cab40c1e94203277258
Allow any value to be passed on the docker_storage_driver field by turning it
into a StringField (was EnumField), and remove the constraints limiting the
values to 'devicemapper' and 'overlay'.
Change the docker storage setup to have a generic setup for all drivers with
the exception of 'devicemapper', which keeps its own specific storage config
function. For all others, do the same we already did for overlay (with two
cases for usage of a cinder volume or not) and simply set the storage driver
in the docker configuration to the value provided in the cluster template.
Change-Id: I9aa8f232ce64ece4d439c0a476f463820a499617
Closes-Bug: #1722522
Andreas Jaeger