gnt-job list: Switch to query2

This brings “gnt-job list” up to the same level as “gnt-instance list”
with filters. Further updates will add more parameters for the most
common filters (e.g. only running jobs).

Also update the man page.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>