add remote_user_variable from wsgi environment, to use set 'remote_us… …  …er_enable 2'

Hello Jean,
this patch allows to check also the wsgi environ dict for a remote user authentication. This is the place where apache puts this information in the fastcgi and scgi case.

It is activated only by setting remote_user_enable  to 2 in shinken specific.
Please tell me if it does not meet coding styles etc. It's working fine here.

Thanks
  Hermann