MB-29858: Increase slow FlusherTask threshold to 1s
MB-29858: Increase slow FlusherTask threshold to 1s

Analysis of recent cluster logs highlights that a significant number
of FlusherTask runtimes exceed the current 400ms limit. For example,
for the following memcached.log over 13% of log files are reporting
slow flusher tasks:

    $ wc -l memcached.log
      991693 memcached.log

    $ grep -c "Slow runtime for 'Running a flusher loop" memcached.log
    134816

As such, increase the threshold from 400ms to 1s.

Change-Id: I0577066305f2c21a10a02a16eb259b84564b51f8
Reviewed-on: http://review.couchbase.org/95243
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Jim Walker <1cd02e31b43620d7c664e038ca42a060d61727b9@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine