cli: robustize abrt-console-notification.sh

- don't show any notifications without a terminal connected to stdout
- don't continue without writable $HOME directory
- forward all error messages to /dev/null

Resolves rhbz#1141485
Related to rhbz#1139001

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Merge pull request #843 from abrt/rhbz1141485_robustize_abrt_console_notification

Robustize abrt-console-notification.sh