zpool initialize functions well for touching every free byte...once.
But if we want to do it again, we're currently out of luck.
So let's add zpool initialize -u to clear it.
Co-authored-by: Rich Ercolani <rincebrain@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes#12451Closes#14873