MINOR: lb: allow redispatch when using consistent hash

Redispatch traditionally only worked for cookie based persistence.

Adding redispatch support for consistent hash based persistence - also
update docs.

Reported by Oskar Stenman on discourse:
https://discourse.haproxy.org/t/balance-uri-consistent-hashing-redispatch-3-not-redispatching/3344

Should be backported to 1.8.

Cc: Lukas Tribus <lukas@ltri.eu>
4 files changed