RabbitMQ 3.7.6-rc.2 发布，AMQP 消息服务器

RabbitMQ 3.7.6-rc.2 已发布，这是常规维护版本的候选版，主要包括错误修复。

本次更新包含如下内容：

Max priority cap for queues is now enforced and set to 255. Applications that rely on a higher number of priorities will break. Such applications must be updated to use no more than 255 priorities.
GitHub issue: rabbitmq-server#1590
Bulk deletion of exclusive queues when their owning connection closes has been optimized.
GitHub issues: rabbitmq/rabbitmq-server#1566, rabbitmq/rabbitmq-server#1513

On Erlang 20.2.3 or later, more optimal memory allocators will be used. On some workloads that leads
to significant reduction in node's RAM consumption. The change is workload-specific, however, on the workloads
tested that do introduce a negative effect (more RAM used) the difference was very small (about 1%).
It is possible to go back to the previous settings, +MBas aoffcbf +MHas aoffcbf +MBlmbcs 5120 +MHlmbcs 5120 +MMmcs 10,
by specifying them in the RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS environment variable.
On Erlang/OTP releases older than 20.2.3 there will be no default changes.
GitHub issue: rabbitmq/rabbitmq-server#1604
connection.closed events now include client-provided connection name and more client details.
That information is in turn available via the rabbitmq_event_exchange.
GitHub issue: rabbitmq-server#1596

await_online_nodes <count> [--timeout <timeout>] is a new command that will wait until the target
node's cluster has at least <count> nodes. The command supports a timeout. It is meant to simplify
cluster provisioning automation and can be used as the very first check performed after starting a node.
Note that the command requires at least one node to be running and reachable.
GitHub issue: rabbitmq-cli#235

When creating a new vhost, user permissions will only be granted to the users that exist in the
internal database. If an external authentication/authorization service is used, the step is skipped.

Virtual host imported from definitions or created via HTTP API will explicitly await for the vhost to initialise
on all cluster nodes.

LDAP connection pool now correctly purges connections in more failure scenarios (e.g. LDAP server restart)
GitHub issue: rabbitmq-auth-backend-ldap#92

201 Created responses are now accepted from HTTP services that back the plugin.
GitHub issue: rabbitmq-auth-backend-http#68