Fix warning about unsupported cookie flags in QEMU driver

The QEMU migration code unconditionally sets the 'persistent'
cookie flag on the source host. The dest host, however, only
allows it during parsing if VIR_MIGRATE_PERSIST_DEST was
set. Make the source host only set it if this flag is
present.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/qemu/qemu_migration.c

@@ -2941,8 +2941,9 @@ cleanup:
         VIR_FORCE_CLOSE(fd);
     }
 
-    cookieFlags |= (QEMU_MIGRATION_COOKIE_PERSISTENT |
-                    QEMU_MIGRATION_COOKIE_NETWORK);
+    cookieFlags |= QEMU_MIGRATION_COOKIE_NETWORK;
+    if (flags & VIR_MIGRATE_PERSIST_DEST)
+        cookieFlags |= QEMU_MIGRATION_COOKIE_PERSISTENT;
     if (ret == 0 &&
         qemuMigrationBakeCookie(mig, driver, vm, cookieout,
                                 cookieoutlen, cookieFlags) < 0) {