generator: tweak how MultiStrOpt defaults are handled

If a MultiStrOpt default is set to None or [], the best thing to do is
just add:

  #multi_str_opt =

to the sample config file.

Change-Id: Ibaee466978870082be47a2135ae3f412d3efd623
Changes imports order to pass H305, enables check

Changes imports order to pass H305 check with hacking 0.9.x
Removes H305 check from ignore line in tox.ini

Change-Id: I47bbe74f4178f46ea21fc37b69f53ea2d148a65e
Merge "Changes imports order to pass H305, enables check"
Merge "generator: tweak how MultiStrOpt defaults are handled"