Add per-opcode results to job processing

This patch changes the definition of a job and introduces per-opcode
results.

First, the result and status fields of a job are condensed into a single
'status' attribute. Then, we introduce an opcode status and one result
list, that allow jobs to return values.

The gnt-job script is also modified to allow these new fields to be
queried.

Note that the patch changes the opcode field to op_list, and it changes
its return value from string to a list of (serialized) opcodes.

Reviewed-by: ultrotter