Created attachment 1075641 [details]
Output of virt-builder -v -x ubuntu-14.04 --size 20G

Description of problem:
When resizing a new guest Ubuntu-14 guest VM,
the builder fails due to a sfdisk error.
"Extended partition already exists.
sfdisk: /dev/sdb: partition 2: failed to set partition type"

Version-Release number of selected component (if applicable):
1.30.0

How reproducible:
100%

Steps to Reproduce:
$ virt-builder ubuntu-14.04 --size 20G

Actual results:
[   1.2] Downloading: http://libguestfs.org/download/builder/ubuntu-14.04.xz
[   1.7] Planning how to build this image
[   1.7] Uncompressing
[   6.7] Resizing (using virt-resize) to expand the disk to 20.0G
virt-resize: error: libguestfs error: part_set_mbr_id: sfdisk --part-type: 
Extended partition already exists.
sfdisk: /dev/sdb: partition 2: failed to set partition type

If reporting bugs, run virt-resize with debugging enabled and include the 
complete output:

  virt-resize -v -x [...]

Expected results:
Same behavior as Fedora 22:
$ virt-builder fedora-22 --size 20G
[   1.2] Downloading: http://libguestfs.org/download/builder/fedora-22.xz
[   1.8] Planning how to build this image
[   1.8] Uncompressing
[   8.1] Resizing (using virt-resize) to expand the disk to 20.0G
[  20.4] Opening the new disk
[  32.1] Setting a random seed
[  32.1] Setting passwords
virt-builder: Setting random password of root to sEIz4Vaf2WykUvQN
[  33.1] Finishing off
                   Output file: fedora-22.img
                   Output size: 20.0G
                 Output format: raw
            Total usable space: 5.4G
                    Free space: 4.6G (86%)

Additional info:
Output of
virt-builder -v -x ubuntu-14.04 --size 20G
attached.