core: log exception when OVF is corrupted

log to error the exception when failing to read the OVF

* move the responsibility for logging error deeper

* throw only 1 checked exception and with the obvious type

* simplify exception stucture

* add debug in case one wants to peek to OVF

Change-Id: Ibc25b6544a698df013fc6d6b2677d798408289a6
Bug-Url: https://bugzilla.redhat.com/1039468
Signed-off-by: Roy Golan <rgolan@redhat.com>