usertools: fix CPU layout for more than 2 threads
usertools: fix CPU layout for more than 2 threads

Current usertools/cpu_layout.py is broken to handle multithreads
of count more than 2 as in IBM powerpc P8 servers.
Below patch addressed this issue.

Also, added minor exception catch on failing to open unavailable
sys file in case of multithread=off configuration in server.

Patch has been verified not to break existing topology configurations
and also not changing anything in current output.

Signed-off-by: Gowrishankar Muthukrishnan <b565c1cabbc104f9755b890159910f97e2efe01a@linux.vnet.ibm.com>
Reviewed-by: Andriy Berestovskyy <5a0adb12ae95814153dc6089b3d01dffbbe8369c@caviumnetworks.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk