MINOR: config: new backend directives: load-server-state-from-file and server-state...

MINOR: config: new backend directives: load-server-state-from-file and server-state-file-name

This directive gives HAProxy the ability to use the either the global
server-state-file directive or a local one using server-state-file-name to
load server states.
The state can be saved right before the reload by the init script, using
the "show servers state" command on the stats socket redirecting output into
a file.