make the dump directories owned by root by default

It was discovered that the abrt event scripts create a user-readable
copy of a sosreport file in abrt problem directories, and include
excerpts of /var/log/messages selected by the user-controlled process
name, leading to an information disclosure.

This issue was discovered by Florian Weimer of Red Hat Product Security.

Related: #1212868

Signed-off-by: Jakub Filak <jfilak@redhat.com>