Allow qemu driver (and hence libvirtd) to load when qemu
user:group does not exist.  The kvm package, which may not
exist on a xen host, creates qemu user:group.

A better (future) solution would be to build the libvirtd
drivers as loadable modules instead of built-in to the
daemon.  Then the qemu driver would only be loaded when needed,
which would never be the case on a xen-only configuration.

Index: libvirt-1.0.5.1/src/qemu/qemu_conf.c
===================================================================
--- libvirt-1.0.5.1.orig/src/qemu/qemu_conf.c
+++ libvirt-1.0.5.1/src/qemu/qemu_conf.c
@@ -435,15 +435,15 @@ int virQEMUDriverConfigLoadFile(virQEMUD
 
     p = virConfGetValue(conf, "user");
     CHECK_TYPE("user", VIR_CONF_STRING);
-    if (p && p->str &&
-        virGetUserID(p->str, &cfg->user) < 0)
-        goto cleanup;
+    if (p && p->str)
+        if (virGetUserID(p->str, &cfg->user) < 0)
+            VIR_WARN("User %s does not exist! Continuing...", p->str);
 
     p = virConfGetValue(conf, "group");
     CHECK_TYPE("group", VIR_CONF_STRING);
-    if (p && p->str &&
-        virGetGroupID(p->str, &cfg->group) < 0)
-        goto cleanup;
+    if (p && p->str)
+        if (virGetGroupID(p->str, &cfg->group) < 0)
+            VIR_WARN("Group %s does not exist! Continuing...", p->str);
 
     GET_VALUE_BOOL("dynamic_ownership", cfg->dynamicOwnership);