Bug 31995: build_holds_queue.pl should check to see if the RealTimeHoldsQueue syspref...

Bug 31995: build_holds_queue.pl should check to see if the RealTimeHoldsQueue syspref is on

The real time hold queue and the build_holds_queue.pl jobs are not 100% compatible in that we should not be running the cron if the real time queue is enabled, this could lead to double server work. It would be good to have a check in build_holds_queue for the RealTimeHoldsQueue syspref and not run the job if the preference is enabled.

There might be times when we'd want to force a run of this job without changing the syspref. To that end we would also want a flag for this job so that system administrators could force the job from the command line if required, overriding this limitation.

Test Plan:
1) Apply this patch
2) Try run misc/cronjobs/holds/build_holds_queue.pl with the -h/--help and -m/--man options
3) Disable RealTimeHoldsQueue
4) Run with no options, should succeed
5) Enable RealTimeHoldsQueue
6) Run with no options, should display a message and not rebuild the
   holds queue
7) Run again with the -f/--force option, should succeed

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>