Use smartmontool's JSON output

[ercpe]

Parsing the output of the smartctl output was more of a poor-man's way to get the SMART information (still easier too implement than figuring out how to get the raw smart values directly from the drive).

Recent versions of smartmontools have a JSON output (via the -j argument) which removes a lot of the guesswork and manual parsing of the output.

• Support (and prefer) the JSON output when calling smartctl
• Fallback to parsing the output if the installed versions does not support the -j argument.