rcutorture: Re-enable testing of dynamic expediting

During boot, normal grace periods are processed as expedited.  When
rcutorture is built into the kernel, it starts during boot and thus
detects that normal grace periods are unconditionally expedited.
Therefore, rcutorture concludes that there is no point in trying
to dynamically enable expediting, do it disables this aspect of testing,
which is a bit of an overreaction to the temporary boot-time expediting.

This commit therefore rechecks forced expediting throughout the test,
enabling dynamic expediting if normal grace periods are processed
normally at any point.

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