nvmet: add support for reporting the host identifier

And fix the Get/Set Log Page implementation to take all 8 bits of the
feature identifier into account.

Signed-off-by: Omri Mann <omri@excelero.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
[hch: used the UUID API, updated changelog]