torture: Make config-fragment filtering RCU-independent

The torture tests need to set specific values for their respective
Kconfig options (e.g., CONFIG_LOCK_TORTURE_TEST), and must therefore
filter any conflicting definitions from the Kconfig fragment
file.  Unfortunately, the code in kvm-build.sh was looking only for
CONFIG_RCU_TORTURE_TEST.  This commit therefore handles the general case
of CONFIG_[A-Z]*_TORTURE_TEST.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>