AzurePersistence can still write segments after having lost lease to another instance

If the SegmentWriteQueue have pending writes while AzurePersistence is unable to renew the lease (both likely caused by connection problems with Azure), and another Oak instance starts and acquire the lease, then the first Oak instance may still be able to write segments to Azure, corrupting the repository.

We need to make sure no writes can happen if the lease has been lost to another instance.