Comment 4 for bug 1880828

Is it possible that qemu-img is timing out? If so, seems like this could be bug 1805256. We are working on a fix for that - the bionic MP is at:
  https://code.launchpad.net/~rafaeldtinoco/ubuntu/+source/qemu/+git/qemu/+merge/383566
And Rafael is staging fixes in:
  https://launchpad.net/~rafaeldtinoco/+archive/ubuntu/lp1805256

Note that the qemu package version 1:2.11+dfsg-1ubuntu7.25 there right now is known to still hang for a different reason. You'll want to wait until he prepares a newer test version, which should be 1:2.11+dfsg-1ubuntu7.27.