request #7239 - LDAP/Tuleap user synchronization no longer retrieve extra attributes

Regression introduced by request #7151 (commit feb42fe)

Before that modification, Tuleap retrieved all LDAP default attributed.
After this patch, if a site use a custom LDAP_UserSync (in
/etc/tuleap/plugins/ldap/site-content/synchronize_user.txt) and rely on extra
paramters for custom synchronization, the process will be broken.

This commit rewrite (with test) the LDAP authentication and ensure that extra
params are fetched if they are defined.

Change-Id: I28ff80b102de9fe1e6be1f79f1583c7f580cfa6b