Improvements to auth_ldap

1. Allow for LDAP one-step login
2. Use ldaps:// protocol for secure mode
3. Fix UnicodeEncodeError in LDAP login
4. Add support for LDAP bind suffix

Further improvements could be made by skipping the LDAP search when the
create_user option is disabled.  This would turn ldap_filter and
ldap_base into optional fields.