devmapper fix usage of pool transaction id 

Fixes Issue: #9257

There are multiple issues with current devmapper usage of pool transaction Id. This patch series tries to fix these.

Details of problem and proposed fix are available in Issue: #9257

Thanks
Vivek
@alexlarsson 

Leaving unused devices in pool will just lead to used space which can't be freed. IMHO, it is a good idea to fix this problem.

You mentioned that you broke down the metafile so that multiple processes could mount in parallel. Are you referring to different threads of daemon or some external process will go through same metadata and mount the device.

Does it apply to device creation/deletion also. If not, then we should not be affected as this transaction logic applies to only device creation/deletion and has nothing to do with device
mounting.