Because of instance locks, after submitting a repair job we weren't able to
set the "pending" tag until at least the first opcode of the job finished.
Introduce a small delay in the repair job so as to allow the subsequent
TAGS_SET job to finish immediately, resulting in faster operation from the
user's point of view.

Make the duration of the delay configurable with --job-delay; if zero,
avoid inserting the TestDelay opcode entirely.

Signed-off-by: Dato Simó <dato@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>