Fix RabbitMQ element clustering start and stop

Prevent upstart respawning from SIGTERM due to post-stop pkill running.

Separate config files out of the install.d script into files to help
readability.

Renumber 40-rabbitmq to 51-rabbitmq and 50-rabbitmq-passwords to
52-rabbitmq-passwords so that ntp runs before these scripts

Graceful start and stop, to prevent split-brain issues. In the non-cluster
case: just restart.

In the cluster case: stop everything gracefully. Start everything. Join
bootstrap node if not bootstrap, otherwise join any node. This prevents getting
two disjoint clusters.

"graceful" means RAM nodes sync with disk nodes before they stop. If they are
stopped unceremoniously, they lose data.

Closes-Bug: #1334314
Change-Id: Ic758256481fdd31d10f4e4a341ae93cb372a0766
Merge "Fix RabbitMQ element clustering start and stop"