HostStatsThread: change way of counting CPUs

There is no /sys/class/cpuid in Ubuntu Server 12.10 64 bit.
Use max(os.sysconf('SC_NPROCESSORS_ONLN'), 1) instead.

The patch is on going work of porting VDSM to Ubuntu
http://www.ovirt.org/VDSM_on_Ubuntu

Change-Id: Ia9e1a104c2241b8f5e8a9b4098530826c3b1677d
Signed-off-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/12815
Reviewed-by: Pradipta Banerjee <bpradip@in.ibm.com>
Tested-by: Pradipta Banerjee <bpradip@in.ibm.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>