Multi target without need for specifying --mongodb.uri

[andreav]

With Prometheus multitarget scraping, it is possible to setup a configuration combining:

• service discovery (like dockerswarm_sd_config)
• relabel_config

to have a completely dynamic multi instance scraping.

Here is an example for Redis Exporter with static_configs and file_sd_configs but it can be realized also with dockerswarm_sd_config to make it completely dynamic.
Redis Exporter adopted a --redis.addr= (note empty value) for indicating multi instance scraping.

This would be a powerful improvement in situations where you need a dynamic configuration.