[core] Option to disable creating HDFS home directory for not first user when login-in

Request to add configuration option to disable creating HDFS home directory for not first user when login.
Based on the following code, if the auth's backends has AllowAllBackend or LdapBackend, we always create HDFS home for the user. HUE-1556 adds this support for LdapBackend and HUE-962 adds this support for AllowAllBackend.

 if is_first_login_ever or 'AllowAllBackend' in backend_names or 'LdapBackend' in backend_names:
          # Create home directory for first user.
          try:
            ensure_home_directory(request.fs, user.username)
          except (IOError, WebHdfsException), e:
            LOG.error(_('Could not create home directory.'), exc_info=e)
            request.error(_('Could not create home directory.'))

It will be better to add a configuration option to disable/enable creating HDFS home directory for AllowAllBackend or LdapBackend(not first user when login). So It will let hadoop administrator better manage the user home directory. The following-up JIRA may add option to set quota on the home directory.