Default number of buckets does not include system buckets

[gshif]

When using default limit, which is 20, for the number of buckets to be returned, GET /buckets endpoint returns 22 buckets, which includes two system buckets _tasks and _monitoring.
If that is intentional then we would need to update swagger doc to mention that default limit value does not include system buckets.
The same happens when setting limit to any other number less or equals to 100 (currently we won't return more than 100 buckets).
One thing is that it is not happening all the time.