核心服务器 Bug 修复：
Process responsible for running the autoheal partition handling strategy
could run into a deadlock with its peers, preventing autoheal from completing.
GitHub issue: rabbitmq-server#1346
Garbage collection of mirrored queue metrics on nodes that did not
host a master or mirror for a queue affected delivery and acknowledgement rates.
This could result in rates being 0 or negative when they should not be.
GitHub issue: rabbitmq-server#1340
Stats emission could prevent queue mirrors from performing garbage collection
and consume memory even when they were empty.
RABBITMQ_DISTRIBUTION_BUFFER_SIZE now can be set via