In reviews we usually check import grouping but it is boring.
By using flake8-import-order plugin, we can avoid this.
It enforces loose checking so it sounds good to use it.
This flake8 plugin is already used in tempest.

Note that flake8-import-order version is pinned to avoid unexpected
breakage of pep8 job.

Setup for unit tests of hacking rules is tweaked to disable
flake8-import-order checks. This extension assumes an actual file exists
and causes hacking rule unit tests.

Change-Id: I12b596820727aeeb379bee16c2bc993dee9eb637

Without this patch, the command 'openstack mapping set <args>' will,
upon success, print the rules for the updated mapping and exit with
return code 1 (failure). This is a problem for scripts and config
management tools that depend on the return code to validate whether the
operation was successful, since even upon success the command returns a
failing error code. Moreover, the behavior of printing the new value is
completely unlike the behavior of any of the 'set' subcommands for
other entities. This patch normalizes the 'mapping set' command by
omitting any return value in the SetMapping take_action() method. This
way the client will only exit with an error code if an exception is
raised, and not upon normal operation.

Change-Id: I610ec3b2fa7561072346d46e49cfc1ae82130e0d

this will better isolate the unit tests from the functional tests.
unfortunately, the "integration" tests had to be lumped into the
"unit" tests since we need the separation in testr.conf

Change-Id: Ifd12198c1f90e4e3c951c73bfa1884ab300d8ded