wic: fix generation of partition UUID

Partition UUID for msdos partitioning is based on a 4 bytes long system identifier. Wic uses random number to generate system identifier. For the numbers starting with 0 partition uuid is shorter, which makes wic images non-bootable as kernel expects 8 charactest in PARTUUID parameter.

Padded system identifier with '0' when generating partition UUID to make it always 8 characters long. This should fix the boot issue.

---
 scripts/lib/wic/plugins/imager/direct.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 7d38ab3..67fd183 100644
@@ -323,7 +323,7 @@ class PartitionedImage():
                 if self.ptable_format == 'gpt':
                     part.uuid = str(uuid.uuid4())
                 else: # msdos partition table
-                    part.uuid = '%0x-%02d' % (self.identifier, part.realnum)
+                    part.uuid = '%08x-%02d' % (self.identifier, part.realnum)
 
     def prepare(self, imager):
         """Prepare an image. Call prepare method of all image partitions."""

2.1.4