[RabbitMQ] add possibility to randomise reconnection intervals

The patch adds a simple pillar for OpenStack services:

  message_queue:
     rabbit_timeouts_random: True

This parameter makes OS services to reconnect to RabbitMQ in a more
wide time span, reducing the peak of reconnections at the same moment,
that in turn increases the probability of successful cluster self-healing.
Also, while here, unhardcoded the kombu_reconnect_delay parameter.

Closes-Bug: PROD-36441
Closes-Bug: PROD-36458
Change-Id: Ic8ca646d359b683865af3f271731fbcd4ec144c4
1 file changed