Provide clearer error when failing to retrieve vm.conf from storage.
Provide clearer error when failing to retrieve vm.conf from storage.

Change-Id: Id7b7d91d30625875856316fb8c4f26cd655ff94f
Bug-Url: https://bugzilla.redhat.com/1434209
Signed-off-by: Jenny Tokar <1acd0034267bdb7277525cbe7ae83185c669ca44@redhat.com>

oVirt/ovirt-hosted-engine-setup,oVirt/ovirt-hosted-engine-setup