Now the code can simply initialize a PartitionInfo from a file and then
call LookupUUIDForLabel on it.
Signed-off-by: Dimitris Karakasilis <dimitris@karakasilis.me>
to be used both here (when trying to find the partition UUID using a
label) and on the kairos side when updating the file after calling
kcrypt to encrypt a partition (which causes the UUID to change).
Signed-off-by: Dimitris Karakasilis <dimitris@karakasilis.me>