Fix parallel make problem.

Fix parallel make problem.

When make is called with, for example,
   "make -j9 install install-system"
i.e. both install and install-systemd targets at the same
line and with high -j value,
then the same install.tmp file was used, and udev rules
ends up in systemd service files, or otherway around.

For more information, see:
  http://www.spinics.net/lists/raid/msg46782.html
  http://bugs.gentoo.org/show_bug.cgi?id=517218

Signed-off-by: NeilBrown <neilb@suse.de>