openstack-ceilometer-compute can't communicate with AMQP

Issue

When no instance is present on the compute node, the AMQP communication might get stripped and reported by monitoring tools. Following can be observed:

• on the computes where no instance is running we have seen that there was no connection to the AMQP
• for those systems the monitoring reported the AMQP connection to be down
• on the compute where we had an instance we also had an AMQP connection
• when we moved an instance to one of the error reported computes and waited for the 10min default ceilometer run, the AMQP connection got established