don't set ylim in histogram charts
don't set ylim in histogram charts

Change-Id: I97b6e1a7f789202f3c279e58d5d712bd504cd2e8
Reviewed-on: http://review.couchbase.org/30499
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Pavel Paulau <dd88eded64e90046a680e3a6c0828ceb8fe8a0e7@gmail.com>

couchbase/cbmonitor,couchbase/cbmonitor