try to delete dump dirs using abrtd in the first step

Only in case where libreport is configured to set dumpdir's owner to
user. Users own dump directories but they cannot modify the dump
location. (Due to #583 : /var/tmp/abrt)

Closes #654

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Signed-off-by: Richard Marko <rmarko@fedoraproject.org>