haraka requires tls certs for:
1. supporting AUTH
2. port 587 support (MSA)
currently, we just reuse the cert for the admin domain. Otherwise,
we have to setup dns etc to get a new cert. While doable, its' not
necessary right now.
This is done because:
1. The box code can install certs for addons (like mail addon) when
required.
2. The box code initialize/teardown addons on demand. This is not planned
currently.