apache: reload when config changes (bugfix)

Apparently the Apache module's intention is to reload apache when config
changes. However, right now there is a notify => Service only on the
$conf-enabled path, which is actually the symlink; while this works for
an initial provisioning, it does not work for config *contents* changes,
as the symlink does not get modified at all. Add a notify to the
$conf-available path as well to address this.

Change-Id: I7cd7f306161b8d92e1c22825be9a81c87333c77c