qemu: Unlock monitor when connecting to dest qemu fails

When migrating a qemu domain, we enter the monitor, send some commands,
try to connect to destination qemu, send other commands, end exit the
monitor. However, if we couldn't connect to destination qemu we forgot
to exit the monitor.

Bug introduced by commit d9d518b1.

src/qemu/qemu_migration.c

@@ -1624,8 +1624,10 @@ qemuMigrationRun(struct qemud_driver *driver,
 
     /* connect to the destination qemu if needed */
     if (spec->destType == MIGRATION_DEST_CONNECT_HOST &&
-        qemuMigrationConnect(driver, vm, spec) < 0)
+        qemuMigrationConnect(driver, vm, spec) < 0) {
+        qemuDomainObjExitMonitorWithDriver(driver, vm);
         goto cleanup;
+    }
 
     switch (spec->destType) {
     case MIGRATION_DEST_HOST: