MINOR: httpclient: allow to configure the timeout.connect

MINOR: httpclient: allow to configure the timeout.connect

When using the httpclient, one could be bothered with it returning
after a very long time when failing. By default the httpclient has a
retries of 3 and a timeout connect of 5s, which can results in pause of
20s upon failure.

This patch allows the user to configure the "timeout connect" of the
httpclient so it could reduce the time to return an error.

This patch helps fixing part of the issue #2269.

Could be backported in 2.7 if needed.