mkfs: more sunit/swidth sanity checking

mkfs: more sunit/swidth sanity checking

This fixes 2 issues with stripe geometry validation.

# mkfs.xfs -d sunit=64,swidth=0 ...
both data sunit and data swidth options must be specified

But I did specify it, I specified 0!

So use cli_opt_set() to detect that it was specified.

But we can't allow the above configuration (in fact it causes
a % 0 later in mkfs), so catch it in the "swidth must be a
multiple of sunit" test a bit further down.

(sunit=0,swidth=0 /is/ valid, it's used to override disk
geometry if desired.)

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>