Add a pid cleaner in case container was killed unexpectedly

Fixes docker-library/wordpress/pull/32
Also, cleaned out the conf files because they were just extra copies.
With `rm -f`, you don't even need the `if` at all. :smile:

```bash
#!/bin/bash
set -e

# Apache gets grumpy about PID files pre-existing
rm -f /var/run/apache2/apache2.pid

exec apache2 -DFOREGROUND
```