osschedproxyd: Disable needless and slow dns lookup

In Python 2.6, BaseHTTPServer.BaseRequestHandler is invoking
socket.getfqdn() after each request, to log the client fully qualified
hostname. If dns is not configured properly, this cause needless delay
after each request.

This patch overrides address_string to return client address, avoiding
the dns lookup.

Change-Id: Id622cfdc07419c8ad52ad88323b10639288c3668
Signed-off-by: Nir Soffer <nsoffer@redhat.com>