Use -nofork when starting bosserver via systemd

Systemd does not expect the started process to fork unless
"Type=forking" is given. Use -nofork to run BOS in foreground and allow
systemd to track its state.

Change-Id: I024be12b410d6b8299edd16f309d816a3df469ed
Reviewed-on: http://gerrit.openafs.org/10087
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: Michael Laß <lass@mail.uni-paderborn.de>
Tested-by: Ken Dreyer <ktdreyer@ktdreyer.com>
Reviewed-by: Ken Dreyer <ktdreyer@ktdreyer.com>