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-1.0.2/src/qemu/qemu_conf.c
===================================================================
--- libvirt-1.0.2.orig/src/qemu/qemu_conf.c
+++ libvirt-1.0.2/src/qemu/qemu_conf.c
@@ -247,7 +247,7 @@ int qemuLoadDriverConfig(virQEMUDriverPt
         goto no_memory;
 
     if (virGetUserID(user, &driver->user) < 0)
-        goto cleanup;
+        VIR_WARN("User %s does not exist! Continuing...", user);
 
     p = virConfGetValue(conf, "group");
     CHECK_TYPE("group", VIR_CONF_STRING);
@@ -255,7 +255,7 @@ int qemuLoadDriverConfig(virQEMUDriverPt
         goto no_memory;
 
     if (virGetGroupID(group, &driver->group) < 0)
-        goto cleanup;
+        VIR_WARN("Group %s does not exist! Continuing...", group);
 
     GET_VALUE_LONG("dynamic_ownership", driver->dynamicOwnership);