Merge remote-tracking branch 'stefanha/block' into staging

Merge remote-tracking branch 'stefanha/block' into staging

# By Kevin Wolf (22) and Peter Lieven (1)
# Via Stefan Hajnoczi
* stefanha/block: (23 commits)
  block: Fix direct use of protocols as driver for bdrv_open()
  qcow2: Gather clusters in a looping loop
  qcow2: Move cluster gathering to a non-looping loop
  qcow2: Allow requests with multiple l2metas
  qcow2: Use byte granularity in qcow2_alloc_cluster_offset()
  qcow2: Prepare handle_alloc/copied() for byte granularity
  qcow2: handle_copied(): Implement non-zero host_offset
  qcow2: handle_copied(): Get rid of keep_clusters parameter
  qcow2: handle_copied(): Get rid of nb_clusters parameter
  qcow2: Factor out handle_copied()
  qcow2: Clean up handle_alloc()
  qcow2: Finalise interface of handle_alloc()
  qcow2: handle_alloc(): Get rid of keep_clusters parameter
  qcow2: handle_alloc(): Get rid of nb_clusters parameter
  qcow2: Factor out handle_alloc()
  qcow2: Decouple cluster allocation from cluster reuse code
  qcow2: Change handle_dependency to byte granularity
  qcow2: Improve check for overlapping allocations
  qcow2: Handle dependencies earlier
  qcow2: Remove bogus unlock of s->lock
  ...