torture: copychunk test suite improvements

torture: copychunk test suite improvements

Allow for large files in test_setup_copy_chunk():
  Write test data in 1M IOs, rather than attempting to do the whole
  thing in one go.

Add copychunk bad resume key test:
  Send a copy chunk request with an intentionally bogus resume key
  (source key handle).

Add copychunk src=dest test:
  Test copychunk requests where the source and destination handles refer
  to the same file.

Add copychunk src=dest overlap test.

Add desired access args to test_setup_copy_chunk().

Add copychunk_bad_access test:
  Open the copychunk source and destination files with differing
  desired_access values. Confirm copychunk response matches 2k8 and 2k12
  behaviour.

Add copy_chunk_src_exceed test:
  Attempts to copy more data than is present in the copychunk source
  file.

Add copy_chunk_src_exceed_multi test:
  Test whether the first chunk in a multi-chunk copychunk request is
  written to disk, where the second chunk is invalid due to src file
  overrun.

Add copy_chunk_sparse_dest test:
  Issue a request where the target offset exceeds the file size, resulting
  in a sparse region.

Add copy_chunk_max_output_sz test.

(cherry picked from commit 456724f05d79733fe805a3209231c565d69d2be3)