Merge branch 'dl/test-must-fail-fixes-4'

Test clean-up.

* dl/test-must-fail-fixes-4:
  t9819: don't use test_must_fail with p4
  t9164: use test_must_fail only on git commands
  t9160: use test_path_is_missing()
  t9141: use test_path_is_missing()
  t7508: don't use `test_must_fail test_cmp`
  t7408: replace incorrect uses of test_must_fail
  t6030: use test_path_is_missing()