HTools: Pass --ignore-soft-errors all the way through

Fixes hail silently ignoring the --ignore-soft-errors flag.

For hspace and tests, the default is set to False (do not force),
like it was before.

The core change is in `allocateOnSingle`/`allocateOnPair`,
which now call `addPriEx force` instead of `addPri` (that one
defaults to `force = False`).