abrt-dump-oops: limit amount of created dirs, add cooldown sleep if exceeded. rhbz#952773

This is a partial backport of 6fc121f145354dd95bb588eb685f1593f5156ca0.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Jiri Moskovcak <jmoskovc@redhat.com>