net-mgmt/rubygem-riemann-*: new ports for the riemann.io suite

Riemann [net-mgmt/riemann] is a streaming event monitoring system
designed for monitoring distributed systems in real time.

This commit introduces the following gems:

• rubygem-riemann-client
• rubygem-riemann-dash
• rubygem-riemann-rabbitmq
• rubygem-riemann-tail
• rubygem-riemann-tools

Which allows connecting to riemann, to set & query events and the index,
to view event status in real-time, whether as a dashboard of events, or
as a classic tail in the terminal. An additional comprehensive set of
integrations for popular tools such as Varnish, Haproxy, nginx,
RabbitMQ, and more, are included in the riemann-tools gem.

More information about Riemann in general is at https://riemann.io/

Reviewed by: romain
Approved by: jrm (mentor)
Differential Revision: https://reviews.freebsd.org/D17710