Re-read the partition table with 'partx -a', rather than 'partx -u'.
This should fix an timing issue where the bootloader installation
fails to mount the EFI partition from a whole disk image since it
is not yet aware of the new partitions (observed with both, the
iscsi and the direct deploy interface).
Change-Id: If5da3075e813ae01df3decf8f0647aba111b0515