Merge stable, change JSON library

[Gsantomaggio]

With this PR is possible to use the auto-cluster plugin with 3.7.x version:

• Merge stable
• Change JSON library
• Rename to rabbitmq_autocluster ( Part of https://github.com/rabbitmq/rabbitmq-autocluster/issues/31 )
• Change format log ( As discussed internally the easier way to fix the log is to use default )
• Replace time_compat functions ( time_compat was removed from master see https://github.com/rabbitmq/rabbitmq-server/issues/546 )
• Replace rand_compat functions ( rand_compat was removed from master see https://github.com/rabbitmq/rabbitmq-server/issues/546 )
• Add rabbitmq depdency
• NOTE about the Docker Image: Change (temporarily) the repo to download the RabbitMQ 3.7.x image, to make easy the tests

Tested on:

• K8s using etcd2
• K8s using StatefulSet Controller
• Consul