rcutorture: Correctly handle CONFIG_RCU_TORTURE_TEST_* options

rcutorture: Correctly handle CONFIG_RCU_TORTURE_TEST_* options

The rcutorture scripting handles the CONFIG_*_TORTURE_TEST Kconfig
options specially, and therefore greps them out of the Kconfig-fragment
files.  Unfortunately, a poor choice of grep pattern means that the
CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP, CONFIG_RCU_TORTURE_TEST_SLOW_INIT,
and CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT Kconfig options are also grepped
out, preventing rcutorture from using them.  This commit therefore fixes
the offending grep pattern to focus only on the CONFIG_*_TORTURE_TEST
Kconfig options.

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