While the endpoint checks should work in all datacenters, only the
current master receives real-world traffic, so we should only check the
logstash hosts in that datacenter.
To this end:
- (partially) refactored the pooler submodule, and renamed it confctl
- Added a confctl.setup_conftool function to standardize the way conftool is setup, and also load its schema.
- Added a confctl.get_master_dc_nodes function that allows filtering a conftool query only including nodes in the current master datacenter
- Modified the canary checks to filter the logstash checks via the aforementioned function
The coupling to conftool availability (which could be concerning in
itself) is very loose: if a proper response can't be obtained, the
unfiltered list will be used and the user will be notified with a warning.