mod_pubsub_serverinfo: implemented all basic features
This commit replaces the earlier proof-of-concept to a solution that:
- reports on remotely-connected domains
- uses disco/info to detect if those domains opt-in
- publishes domain names for remote domains that do so
- caches the disco/info response
---
summary: STARTTLS failure test
---
This module responds to `<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>` with
`<failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>`, in order to test
how clients and server behave.
See [RFC6120 Section 5.4.2.2](https://xmpp.org/rfcs/rfc6120.html#rfc.section.5.4.2.2)