FreeBSD: Add option to rewind checkpoint while importing root pool
This option is used by FreeBSD boot loader.
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Mariusz Zaborski <oshogbo@vexillium.org>
Closes #10738