autofs: correct QA issues with orphaned systemd files

If we build a project without systemd support on a system that has systemd
enabled, the following QA items get flagged:

  /lib
  /lib/systemd
  /lib/systemd/system
  /lib/systemd/system/autofs.service

Trying to keep the solution to the problem as contained as possible in a
way that may be accepted up-stream by adding an optional parameter to the
--with-systemd flag.

Signed-off-by: Joe MacDonald <joe@deserted.net>