Don't check whether all partitions of the restore device are not mounted #849
Description
With release 0.7 it's possible to specify the partitions to restore for a partition oriented backup.
Following usecase of option -T and -0 is not supported right now:
Restore device hast 3 partitions. On partition 3 the backups are stored and the partition is mounted in order to restore the first 2 paritions. Then a restore is rejected because raspiBackup detects there is a mounted partition 3 when only the first two partitions should be restored with option -T. But because partition 3 is not restored it can be mounted.
Note: It's not a good idea to have the backups on the same device as the OS - but there are usecases when it makes sense. For example when backup is asynchronously saved on a NAS. A restore from a local disk will be much faster than a restore from a NAS.