qemu.tests.physical_resources_check: update get cpu number method for windows guest

Add new function get_cpu_number() to get cpu sockets/cores/threads number.

Signed-off-by: Shuping Cui <scui@redhat.com>
Merge pull request #29 from spcui/physical_resources_check

qemu.tests.physical_resources_check: update get cpu number method for windows guest