[BUG] Don't increment server connections too much + fix retries

[BUG] Don't increment server connections too much + fix retries

Commit 98937b875798e10fac671d109355cde29d2a411a while fixing
one bug introduced another one. With "retries 4" and
"option redispatch" haproxy tries to connect 4 times to
one server server and 1 time to a second one. However
logs showed 5 connections to the first server (the
last one was counted twice) and 2 to the second.

This patch also fixes srv->retries and be->retries increments.

Now I get: 3 retries and 1 error in a first server (4 cum_sess)
and 1 error in a second server (1 cum_sess) with:
 retries 4
 option redispatch

and: 4 retries and 1 error (5 cum_sess) with:
 retries 4

So, the number of connections effectively served by a server is:
 srv->cum_sess - srv->failed_conns - srv->retries

(cherry picked from commit 626a19b66f769a87e7c995267ccedf14149e03b3)