xmlrpc: [Fix] Use correct base class for parsing request

Previously we always used SecureXMLRPCServer.parse_request, even when
using SimpleXMLRPCServer. That happened to work since both inherit
parse_request from BaseHTTPServer. This patch use the correct base
class, so if one of them will override parse_request, we use the correct
method.

Note: Without this fix ssl=false does not work on python 2.7

Change-Id: I4ef737c02afb97580179f381e0f227ee94e1383f
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1074063
Signed-off-by: Gustavo Pedrosa <gustavo.pedrosa@eldorado.org.br>
Reviewed-on: http://gerrit.ovirt.org/24289
Reviewed-on: http://gerrit.ovirt.org/25524
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>