qemu: fix one more race on undefining and create

[1] closes gap in virDomainObjListRemove so that concurrent thread can
not step in and obtain the domain while domain is temporary unlocked. But
there is another gap exist:

thread B - executes create API
thread C - executes undefine API

- thread A executes some job on domain
- threads B and C obtains domain from list and wait for job condition
- thread A finishes its job and C grabs job condition, removes domain
  from list and finishes
- thread B grabs job condition and start the domain, unfortunately
  is not in the list already

[1] commit c7d1c139ca
Author: Martin Kletzander <mkletzan@redhat.com>
Date:   Thu Dec 11 11:14:08 2014 +0100

    qemu: avoid rare race when undefining domain

Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy@openvz.org>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>

src/qemu/qemu_domainjob.c

@@ -849,6 +849,16 @@ qemuDomainObjBeginJobInternal(virQEMUDriver *driver,
     if (!nested && !qemuDomainNestedJobAllowed(&priv->job, job))
         goto retry;
 
+    if (obj->removing) {
+        char uuidstr[VIR_UUID_STRING_BUFLEN];
+
+        virUUIDFormat(obj->def->uuid, uuidstr);
+        virReportError(VIR_ERR_NO_DOMAIN,
+                       _("no domain with matching uuid '%s' (%s)"),
+                       uuidstr, obj->def->name);
+        goto cleanup;
+    }
+
     ignore_value(virTimeMillisNow(&now));
 
     if (job) {