Oh god, python-ldap is crap...
* add better unit test
* correct params name
* correct exception handling
* disable testConnectSSLNoCheck (impossible to test with a certificate
previously defined)
* change parameters name for Backend Ldap
* fix default value handling in backends get_param
* correct exception in backends get_param
* fix syntaxe error
* add backend name in test_BackendLdap.py