MFC r350477: Feature-complete NVMe Namespace Management.

MFC r350477: Feature-complete NVMe Namespace Management.

This adds several previously missed but important subcommands to list
namespaces and controllers.  It also fixes few previously added but
just found with real testing to be broken subcommands.

Also while there, add possibility to explicitly specify nsid for
`nvmecontrol identify` subcommand.  It may be useful to specify nsids
not having own devices, for example 0xffffffff, or just newly created
ones.