MEDIUM: check: server states and weight propagation re-work

The server state and weight was reworked to handle
"pending" values updated by checks/CLI/LUA/agent.
These values are commited to be propagated to the
LB stack.

In further dev related to multi-thread, the commit
will be handled into a sync point.

Pending values are named using the prefix 'next_'
Current values used by the LB stack are named 'cur_'
19 files changed