harvest-vmcore: properly handle inaccessible dir error

Related to rhbz#1032511

rmarko: added missing newlines to sys.stderr.write calls

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Merge pull request #798 from abrt/rhbz1032511_vmcore_oserror

harvest-vmcore: properly handle inaccessible dir error