radosgw-admin: fix subuser modify

Shouldn't check for empty access key when modifying swift user, also
set correct fields when updating swift keys.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: subuser creation can be idempotent

No real reason to check for existing subuser before (re)creating it.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
radosgw-admin: don't always generate access key for subusers

Only generate key for subuser if one was not specified for it, and only
when creating a subuser.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
Merge pull request #1630 from ceph/wip-7450

Wip 7450

Reviewed-by: Josh Durgin <josh.durgin@inktank.com>