Add a regression test for PR 221234
etc/mtree/BSD.tests.dist
tests/sys/cddl/zfs/tests/cli_root/Makefile
tests/sys/cddl/zfs/tests/cli_root/zfs_diff/...
Add an automated test that checks the typical output of "zfs diff".
The is the first and only automated test for "zfs diff". It
currently fails for a file that gets moved to a new directory.
PR: 221234
Sponsored by: Spectra Logic Corp