ep-engine Slow tasks log not recording any slow tasks

Description

During investigation of MB-24107, I noticed that the code which determines if a task is 'slow' is using the wrong units - seconds instead of microseconds:

addLogEntry(currentTask->getTaskable().getName() +

    to_string(currentTask->getDescription()),

    q->getQueueType(), runtime, startReltime,

    (runtime > std::chrono::seconds(

        currentTask->maxExpectedDuration())));

This bug was introduced by http://review.couchbase.org/69899, which was first included in 4.6.0.

Impact

This has no impact on customer-visible functionality, but it does mean our logging of slow tasks is essentially broken - it'll only kick in for tasks taking longer than 3600 seconds (1 hour), instead of the expected 3.6milliseconds (which is probably too low anyway...)