ocp-nvme: Add a different formatting for JSON output

ocp-nvme: Add a different formatting for JSON output

The current OCP JSON format for the SMART extended log page is not
condusive to metric collection via tools like Prometheus. So we add a
new output mode that uses all lower case and underscores (instead of
spaces). This should help with metric collection. At the same time we
clean up some of the field names. We add a new argument
(--output-format-version) to allow us to select which output version
we want. Documentation updated to reflect this change and mark this as
experimental.

Fixes #2577.

Signed-off-by: Stephen Bates <sbates@raithlin.com>