Unified ldap_initialize() function
    
    Replace all ldap.initialize() calls with a helper function
    ldap_initialize(). It handles cacert and cert validation correctly. It
    also provides a unique place to handle python-ldap 3.0 bytes warnings in
    the future.
    
    Fixes: https://pagure.io/freeipa/issue/7411
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>