[FIX] strip spaces from user name as they will probably be ignored by ldap's search

According to http://tools.ietf.org/html/rfc4518, caseIgnoreMatch (the matching operator commonly used for uid) also discards 'insignificant spaces'. The informative section states that this includes leading and trailing spaces.

This leads to logging in as 'joe ' being mapped to ldap's 'joe', but odoo will create a new user called 'joe ', which is probably not what we want.