Some buckets are leaked

[marta-lokhova]

Looks like fixing #2286 was not enough, and we still have bucket number constantly fluctuating (with total number of files being over expected 31). Checking the logs, the number of buckets referenced by the bucketlist, publishqueue and LCL is correct, so it must be failing the refcount == 1 check in forgetUnreferencedBuckets

[MonsieurNicolas]

Here's a gist of an increase in number of shared-buckets https://gist.github.com/MonsieurNicolas/5436a26ac3c06e2edbb010d45aaab596 (not sure there is anything in there useful)