Propagator: Fix t8.pl

Propagator: Fix t8.pl

The test sets OWNCLOUD_MAX_PARALLEL to 1 to disable parallelism.
But since the max amount of parallelism is twice as much, that does not
work.
So change the way we compute the hardMaximumActiveJob: Use the value of
OWNCLOUD_MAX_PARALLEL to maximize this amount and base the maximum amount
of transfer jobs on it instead of the other way.

A result of this change is that, in case of bandwidth limit, we keep the
default of 6 non-transfer jobs in parallel. I believe that's fine since
the short jobs do not really use bandwidth, so we can still keep the same
amount of small jobs.