Avoid trying to send emails to users without emails

Log a warning when this happens. Also add some other logging.

Change-Id: I86d9b38d012a1b73d6247b1fc43081c75859c754
Auto accept any missing host keys

There's nothing particularly sensitive going on here, and this is
easier than trying to set up the keys being in the known_hosts file
via puppet. It also makes development easier.

Change-Id: Ib5cd47b17c10606742575f92543360eddd2ee2e3