tests: ts_scsi_debug_init skip instead of die

tests: ts_scsi_debug_init skip instead of die

If any of these modprobe commands fails then it's not a broken test.
ALso ts_die often does not work correctly from subtests which should
be fixed someday too.

BTW modprobe dry-run (even the real modprobe) is not reliable.
Moreover now we respect blacklisted modules (-b).

This error handling is not only useful to let the test-suite succeed
on broken systems but also to not fail all "scsi_debug tests" after
just one of them failed to umount something.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>