MEDIUM: server: Inherit CLI weight changes and agent-check weight responses

When agent-check or CLI command executes relative weight change this patch
propagates it to tracking server allowing grouping many backends running on
same server underneath. Additionaly in case with many src IPs many backends
can have shared state checker, so there won't be unnecessary health checks.

[wt: Note: this will induce some behaviour change on some setups]
3 files changed