Ensure nodeinfo struct is initialized to zero

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>

src/nodeinfo.c

@@ -389,11 +389,6 @@ int linuxNodeInfoCPUPopulate(FILE *cpuinfo,
     char *sysfs_nodedir = NULL;
     char *sysfs_cpudir = NULL;
 
-    nodeinfo->cpus = 0;
-    nodeinfo->mhz = 0;
-    nodeinfo->cores = 0;
-    nodeinfo->nodes = 0;
-
     /* Start with parsing CPU clock speed from /proc/cpuinfo */
     while (fgets(line, sizeof(line), cpuinfo) != NULL) {
 # if defined(__x86_64__) || \
@@ -870,6 +865,8 @@ int nodeGetInfo(virConnectPtr conn ATTRIBUTE_UNUSED, virNodeInfoPtr nodeinfo)
 {
     virArch hostarch = virArchFromHost();
 
+    memset(nodeinfo, 0, sizeof(*nodeinfo));
+
     if (virStrcpyStatic(nodeinfo->model, virArchToString(hostarch)) == NULL)
         return -1;