Sentinel: down-after-milliseconds is not master-specific.

addReplySentinelRedisInstance() modified so that this field is displayed
for all the kind of instances: Sentinels, Masters, Slaves.
Sentinel: propagate down-after-ms changes to slaves and sentinels.
Sentinel: instance_is_killed proc added to sentinel.tcl.
Sentinel test: foreach_instance_id implements 'break'.
Sentinel test: 02 unit better coverage + refactoring.