rcutorture: Add RCU-tasks tests to default rcutorture list

Although the test cases have been added, they must be specified explicitly
via the kvm.sh --configs argument in order to run them.  This commit
therefore adds the RCU-tasks tests to the CFLIST so that they will be
run automatically by default.

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