8942 zfs promote .../%recv should be an error

8942 zfs promote .../%recv should be an error

illumos/illumos-gate@add927f8c8d101e16c23eb9cd270be4fd7edf7d5

Reported on the ZFSonLinux https://github.com/zfsonlinux/zfs/issues/4843,
fixed by https://github.com/zfsonlinux/zfs/pull/6339:

If we are in the middle of an incremental zfs receive, the child .../%recv
will exist. If you concurrently run zfs promote .../%recv, it will "work",
but then zfs gets confused. For example, there's no obvious way to destroy
the containing filesystem (because it is now a clone of its invisible child).

Attempting to do this promote should be an error. We could fix this by
having zfs_ioc_promote() check if zc_name contains a %, similar to
zfs_ioc_rename().

Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Dan McDonald <danmcd@joyent.com>
Author: loli10K <ezomori.nozomu@gmail.com>