Use unique names for VULs, also return 0 on success

Use unique names for VULs, also return 0 on success

Previously nvme_log_id_to_string returned "WDC Vendor Unique Log ID" if
it was any vendor unique log ID. This causes problems when requesting
JSON output, as only the final vendor unique log ID would be shown.
Instead, append the log id to the string making each unique.

Also, wdc_log_page_directory previously returned whatever the
output_format was. Instead return 0 if the format was valid.

Signed-off-by: Brandon Paupore <brandon.paupore@wdc.com>