Add missing log for getStatistics in XMLRPC interface

All methods exported to XMLRPC interface has own info log, when is invoked.
Only getStatistics was missing this log info.

Change-Id: I0021fae11cb9c9efcd2c59e567ec3263a3693d21
Signed-off-by: Martin Pavlasek <mpavlase@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34712
Reviewed-by: Adam Litke <alitke@redhat.com>