tools/workqueue: Add rescuers printing to wq_dump.py

Retrieving rescuers information (e.g., affinity and name) is quite
useful when debugging workqueues configurations.

Add printing of such information to the existing wq_dump.py script.

Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>