Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Incorporate feedback from bde@ based on r252672 changes:

* Use 0/1 instead of sysexits. Man pages are confusing on this topic,
but 0/1 is sufficient for nvmecontrol.
* Use err function family where possible instead of fprintf/exit.
* Fix some typing errors.
* Clean up some error message inconsistencies.

Sponsored by: Intel
Submitted by: bde (parts of firmware.c changes)
MFC after: 3 days

Ensure that a device node is specified when invoking the identify or reset
commands.

Also improve the checking of device node names, so that better error
messages are displayed when incorrect names are specified.

Sponsored by: Intel
MFC after: 3 days

Break out code related to the reset command into a separate source file.

Sponsored by: Intel
MFC after: 3 days