Fix the API definition for cpu tune methods

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1120246
Change-Id: I236af8141e0981a9af680e35860183579f916609
Signed-off-by: Martin Sivak <msivak@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29497
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/30068
Reviewed-by: Francesco Romani <fromani@redhat.com>