A task has to get the SchedulerLock to remove itself from the
Scheduler list. This doesn't work, if the Task is static, as the
static Scheduler might be destroyed earlier. In this case we fail
with the following backtrace:

 #0 SchedulerMutex::acquire
 #1 Task::~Task
 #2 __run_exit_handlers

Thanks to Michael Stahl to catching this backtrace.

As a workaround this marks static tasks, so they ignore the
SchedulerMutex in the destructor, We also mark all scheduled Tasks
as "static" in DeInitScheduler, as their cleanup was already done.

In the end all Tasks should be removed from static objects.

Change-Id: I38be3206378b9449193efaccbc96896ac8de9478
Reviewed-on: https://gerrit.libreoffice.org/42574Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>