Block layer patches

# gpg: Signature made Thu 11 May 2017 10:31:37 AM EDT
# gpg:                using RSA key 0x7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* kwolf/tags/for-upstream: (58 commits)
  MAINTAINERS: Add qemu-progress to the block layer
  qcow2: Discard/zero clusters by byte count
  qcow2: Assert that cluster operations are aligned
  qcow2: Optimize write zero of unaligned tail cluster
  iotests: Add test 179 to cover write zeroes with unmap
  iotests: Improve _filter_qemu_img_map
  qcow2: Optimize zero_single_l2() to minimize L2 churn
  qcow2: Make distinction between zero cluster types obvious
  qcow2: Name typedef for cluster type
  qcow2: Correctly report status of preallocated zero clusters
  block: Update comments on BDRV_BLOCK_* meanings
  qcow2: Use consistent switch indentation
  qcow2: Nicer variable names in qcow2_update_snapshot_refcount()
  tests: Add coverage for recent block geometry fixes
  blkdebug: Add ability to override unmap geometries
  blkdebug: Simplify override logic
  blkdebug: Add pass-through write_zero and discard support
  blkdebug: Refactor error injection
  blkdebug: Sanity check block layer guarantees
  qemu-io: Switch 'map' output to byte-based reporting
  ...
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>