replay: bh scheduling fix

This patch fixes scheduling of bottom halves when record/replay is enabled.
Now BH are not added to replay queue when asynchronous events are disabled.
This may happen in startup and loadvm/savevm phases of execution.

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
