Merge branch 'qemu-disk-size' into 'master'

Add an optional 6th parameter to autopkgtest-build-qemu, to force a specific image size

See merge request !49
3 jobs for master in 8 minutes and 50 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Test
passed #219427
quicktests

00:01:50

passed #219428
tests-sid

00:08:49

passed #219429
tests-stretch

00:07:34