Allow for '-o feature@<feature>=disabled' on the command line

Allow for '-o feature@<feature>=disabled' on the command line

Sometimes it is desirable to specifically disable one or several
features directly on the 'zpool create' command line.

$ zpool create -o feature@<feature>=disabled ...

Original-patch-by: Turbo Fredriksson <turbo@bayour.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #3460
Closes #5142
Closes #5324