vmcore: properly configure Augeas

Configure Augeas to parse only required configuration files:
- /etc/mtab
- /ect/kdump.conf

Related to rhbz#1054158

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Merge pull request #791 from abrt/rhbz1054158_optimal_augeas

vmcore: properly configure Augeas