Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches

# gpg: Signature made Tue 13 Feb 2018 17:03:11 GMT
# gpg:                using RSA key 7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream: (55 commits)
  iotests: Add l2-cache-entry-size to iotest 137
  iotests: Test downgrading an image using a small L2 slice size
  iotests: Test valid values of l2-cache-entry-size
  qcow2: Allow configuring the L2 slice size
  qcow2: Rename l2_table in count_cow_clusters()
  qcow2: Rename l2_table in count_contiguous_clusters_unallocated()
  qcow2: Rename l2_table in count_contiguous_clusters()
  qcow2: Rename l2_table in qcow2_alloc_compressed_cluster_offset()
  qcow2: Update qcow2_truncate() to support L2 slices
  qcow2: Update expand_zero_clusters_in_l1() to support L2 slices
  qcow2: Prepare expand_zero_clusters_in_l1() for adding L2 slice support
  qcow2: Read refcount before L2 table in expand_zero_clusters_in_l1()
  qcow2: Update qcow2_update_snapshot_refcount() to support L2 slices
  qcow2: Prepare qcow2_update_snapshot_refcount() for adding L2 slice support
  qcow2: Update zero_single_l2() to support L2 slices
  qcow2: Update discard_single_l2() to support L2 slices
  qcow2: Update handle_alloc() to support L2 slices
  qcow2: Update handle_copied() to support L2 slices
  qcow2: Update qcow2_alloc_cluster_link_l2() to support L2 slices
  qcow2: Update qcow2_get_cluster_offset() to support L2 slices
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>