torture: Add task state to writer-task stall printk()s

This commit adds a dump of the scheduler state for stalled rcutorture
writer tasks.  This addition provides yet more debug for the intermittent
"failures to proceed", where grace periods move ahead but the rcutorture
writer tasks fail to do so.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>