xmpp: Fix regression, initial letsencrypt support

The 1st commit fixes an error that I introduced :( when switching to ruamel.yaml. Only tls should be set to false (on http bind port, for jwchat), not starttls.

The 2nd commit adds preliminary support for using a letsencrypt certificate with ejabberd. The configuration is done automatically when the LE cert is obtained, if the domain for the cert matches ejabberd's host list.