Use lvconvert --repair in dmeventd DSO (mornfall)

Use lvconvert --repair in dmeventd DSO (mornfall)

This means two things:

1) Non-mirrored LVs will be no longer affected by mirror monitoring. (Before,
if you had a LV that went partially missing on a VG where a mirror leg failed,
this LV would be removed automatically by dmeventd... Probably not an
unrecoverable dataloss bug, but still quite unpleasant.)

2) If enough parallel PV space is available at the time of the mirror failure,
the failed devices will be automatically replaced using this spare space. Which
(and whether) free space may be used is still not configurable, but is a
planned feature. Since it is relatively easy to undo the action by converting
the mirror manually, I don't consider this to be a showstopper. In fact, I
think the compromise is much better than what we have now.