mom.d: make CpuTuneEnabled True by default

we should ship vdsm with that policy enabled otherwise cpu tuning isn't
taking place at all as the policy isn't evaluated.

future: control this policy parameter at runtime as well

Change-Id: I7a602b8d50583b9cd16ef202f285c6a9897fa209
Bug-Url: https://bugzilla.redhat.com/1143992
Signed-off-by: Roy Golan <rgolan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/35330
Reviewed-by: Martin Sivák <msivak@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>