When linuxNodeInfoCPUPopulate() method triggered use of an
uninitialize value, since it did not initialize the 'sockets'
field in the virNodeInfoPtr struct:

==30020== Conditional jump or move depends on uninitialised value(s)
==30020==    at 0x5125DBD: linuxNodeInfoCPUPopulate (nodeinfo.c:513)
==30020==    by 0x51261A0: nodeGetInfo (nodeinfo.c:884)
==30020==    by 0x149B9B10: qemuCapsInit (qemu_capabilities.c:846)
==30020==    by 0x14A11B25: qemuCreateCapabilities (qemu_driver.c:424)
==30020==    by 0x14A12426: qemuStartup (qemu_driver.c:874)
==30020==    by 0x512A7AF: virStateInitialize (libvirt.c:822)
==30020==    by 0x40DE04: daemonRunStateInit (libvirtd.c:877)
==30020==    by 0x50ADCE5: virThreadHelper (virthreadpthread.c:161)
==30020==    by 0x328CA07D14: start_thread (pthread_create.c:308)
==30020==    by 0x328C6F246C: clone (clone.S:114)
(happened twice)

        if (socks > nodeinfo->sockets)    <--- here
            nodeinfo->sockets = socks;

Rather than doing this for each field, just make the caller memset
the entire struct to zero.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>