Leverage repmgr's built-in health checks

[davissp14]

repmgr node check

Node "fdaa:0:2e26:a7b:c850:fa7a:5336:2":
	Server role: OK (node is primary)
	Replication lag: OK (N/A - node is primary)
	WAL archiving: OK (0 pending archive ready files)
	Upstream connection: OK (N/A - node is primary)
	Downstream servers: OK (2 of 2 downstream nodes attached)
	Replication slots: OK (2 of 2 physical replication slots are active)
	Missing physical replication slots: OK (node has no missing physical replication slots)
	Configured data directory: OK (configured "data_directory" is "/data/postgresql")

[guillaumervls]

Being addressed in #142 (paused - reopen to pick back up)

[benwaffle]

would this also return an error for paused nodes?