qemu: error message should show uri instead of (null)

Fix pointer for error message uri if domain migration fails.

BZ# 730244

src/qemu/qemu_migration.c

@@ -2104,7 +2104,7 @@ static int doPeer2PeerMigrate(struct qemud_driver *driver,
     qemuDomainObjExitRemoteWithDriver(driver, vm);
     if (dconn == NULL) {
         qemuReportError(VIR_ERR_OPERATION_FAILED,
-                        _("Failed to connect to remote libvirt URI %s"), uri);
+                        _("Failed to connect to remote libvirt URI %s"), dconnuri);
         return -1;
     }