Fix inconsistency in the LUXI protocol w.r.t. args

This inconsistency was found during rebalancing. Hbal failed because,
Ganeti couldn't load the opcode. After digging through the cause, an
inconsistency with the "args" field in the LUXI protocol was triggered
by the TemplateHaskell side where it's done uniformed.

For SubmitJob and SubmitManyJobs we treat args as one argument,
containing the job definition. In every other LUXI call args is actually
a list of arguments. This patch fixes this consistency.

This change is NOT backwards compatible.

Signed-off-by: René Nussbaumer <rn@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>