Types default values handeling cleanup

Hello,

I went over all default the types in `cdist/types/` and I removed relics from when default types didn't exist.

I just replaced the pattern:
```bash
if [ -f "$__object/parameter/NAME" ]
then
   NAME="$(cat "$__object/parameter/NAME")"
else
   NAME="DEFAULT_VALUE"
fi
```

By:
```bash
NAME="$(cat "$__object/parameter/NAME")"
```
and putting `DEFAULT_VALUE` in `parameter/default/NAME`.