[PATCH] rcutorture: renice to low priority

Make the box usable for interactive work when running the RCU torture test,
by renicing the RCU torture-test threads to +19 by default.  Kthreads run
at nice -5 by default.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>