xmlrpc: Disable unwanted BaseHTTPServer logging

BaseHTTPServer log incoming requests to stderr, which is redirected to
/dev/null in production. During the tests, stderr is used to display
test results. In both cases, the default http logging is useless, and we
have our own logging.

Change-Id: I83ad9723854a4646cc2a5cf23e1a335a82d4f94f
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28772
Reviewed-by: Piotr Kliczewski <piotr.kliczewski@gmail.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>