Comment 7 for bug 1698337

This fix did not work:
http://logs.openstack.org/72/472872/13/check/gate-octavia-v1-dsvm-scenario-multinode/170affe/logs/devstacklog.txt.gz#_2017-06-17_20_28_14_429

2017-06-17 20:28:14.421 | 2017-06-17 20:28:14.421 INFO diskimage_builder.block_device.utils [-] Calling [sudo kpartx -avs /dev/loop0]
2017-06-17 20:28:14.429 | 2017-06-17 20:28:14.429 INFO diskimage_builder.block_device.utils [-] Calling [sudo udevadm settle]
2017-06-17 20:28:14.444 | 2017-06-17 20:28:14.444 DEBUG diskimage_builder.block_device.level2.mkfs [-] Creating fs command [['mkfs', '-t', u'ext4', u'-i', u'4096', u'-J', u'size=64', '-L', u'cloudimg-rootfs', '-U', 'b66194c0-3491-4dfa-9545-4fd1c614c5f4', '-q', u'/dev/mapper/loop0p1']] create /opt/stack/new/diskimage-builder/diskimage_builder/block_device/level2/mkfs.py:130
2017-06-17 20:28:14.444 | 2017-06-17 20:28:14.444 INFO diskimage_builder.block_device.utils [-] Calling [sudo mkfs -t ext4 -i 4096 -J size=64 -L cloudimg-rootfs -U b66194c0-3491-4dfa-9545-4fd1c614c5f4 -q /dev/mapper/loop0p1]
2017-06-17 20:28:14.464 | 2017-06-17 20:28:14.464 DEBUG diskimage_builder.block_device.utils [-] exec_sudo: The file /dev/mapper/loop0p1 does not exist and no size was specified. exec_sudo /opt/stack/new/diskimage-builder/diskimage_builder/block_device/utils.py:120