vmcore: catch IOErrors and OSErrors

Perhaps some temporary data cleaner removed problem directory while the hook
was still using in.

Resolves: rhbz#1077241

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Merge pull request #883 from abrt/rhbz1077241_vmcore_low_level_errors

vmcore: catch IOErrors and OSErrors