torture: Make thread detection more robust by using lspcu

For consecutive numbers the lscpu command collapses the output and just
shows the range with start and end. The processors are numbered that
way on POWER8.

    $ sudo ppc64_cpu --smt=8
    $ lscpu | grep '^NUMA node'
    NUMA node(s):                    2
    NUMA node0 CPU(s):               0-79
    NUMA node8 CPU(s):               80-159

This causes the heuristic to detect the number threads per core, looking
for the number after the first comma, to fail, and QEMU aborts because of
invalid arguments.

    $ lscpu | grep '^NUMA node0' | sed -e 's/^[^,-]*(,|\-)\([0-9]*\),.*$/\1/'
    NUMA node0 CPU(s):               0-79

But the lscpu command shows the number of threads per core:

    $ sudo ppc64_cpu --smt=8
    $ lscpu | grep 'Thread(s) per core'
    Thread(s) per core:              8
    $ sudo ppc64_cpu --smt=off
    $ lscpu | grep 'Thread(s) per core'
    Thread(s) per core:              1

This commit therefore directly uses that value and replaces use of grep
with "sed -n" and its "p" command.

Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>