Add a regression test for PR 225546

If a pool contains a replacing vdev with a spare child, then any "zpool
add" command will fail. It doesn't matter whether you're adding a
regular vdev, log, cache, or spare vdev. The bug is in get_replication
in zpool_vdev.c in the zpool command.

tests/sys/cddl/zfs/tests/cli_root/zpool_add/Makefile
tests/sys/cddl/zfs/tests/cli_root/zpool_add/zpool_add_010_pos.ksh
tests/sys/cddl/zfs/tests/cli_root/zpool_add/zpool_add_test.sh
Add a test case that creates a pool with replacing vdev that has
a spare child, then attempts to add another spare.

tests/sys/cddl/zfs/include/commands.txt
Add an alias for /usr/bin/timeout

PR: 225546
Sponsored by: Spectra Logic Corp