* Avoid waiting for external drive unnecessarily
Even though the condition to start hassos-data.service is not met (the
file /mnt/overlay/data-move is not there by default), it seems that
systemd waits for the dependencies for hassos-data.service. Don't
Require or Wants any dependencies which might not be present by
default.
* Use systemd to wait for partition using partlabel device
* Use sfdisk which allows to wipe filesystem signatures
Even though we zap the partition table using sgdisk, the file system
superblock (which contains the file system label) does survive. This
can cause problems when trying to reuse a disk previously already
labeled using hassos-data: It might take precendence on next boot
over the existing data partition on the eMMC.
Make sure to clean all file system signatures using sfdisk.
* Make the datactl command more robust
Validate target disk (partition) size to avoid a copy attempt which will
fail. If e2image operation fails, make sure the leftover copy is not
regonized as data partition.
* Fix hassos-data service device unit dependencies
* Rewrite datactl command
Prepare the target partition as part of the datactl command. Rely on
partlabel for the target disk since we are always using GPT on the
target disk. Use systemd and partlabel mechanism to wait and find
the target data disk. Keep using the file system label to identify
the source disk.
Also use e2image instead of raw dd to move data. This should
speed up the processes significantly.
* Fix corner case when reusing same disk again
