Merge branch 'dl/test-must-fail-fixes'

Merge branch 'dl/test-must-fail-fixes'

Test clean-up.

* dl/test-must-fail-fixes:
  t1507: inline full_name()
  t1507: run commands within test_expect_success
  t1507: stop losing return codes of git commands
  t1501: remove use of `test_might_fail cp`
  t1409: use test_path_is_missing()
  t1409: let sed open its own input file
  t1307: reorder `nongit test_must_fail`
  t1306: convert `test_might_fail rm` to `rm -f`
  t0020: use ! check_packed_refs_marked
  t0020: don't use `test_must_fail has_cr`
  t0003: don't use `test_must_fail attr_check`
  t0003: use test_must_be_empty()
  t0003: use named parameters in attr_check()
  t0000: replace test_must_fail with run_sub_test_lib_test_err()
  t/lib-git-p4: use test_path_is_missing()