Mail binary good/bad message to admins upon deploy, for pg and django_monolith

First time writing fabric, so please review my use.

Questions/notes:

 - I'm not sure how to best test this.
 - Depends on bumping `corehq` submodule to get the mail_admins management command.
 - Is `sudo` necessary? This command does not really need privs, but all commands in the current `fabfile.py` seem to use `sudo`.
 - Could add a timestamp, githash, commit message, or something to the subject to ensure each deploy is a separate gmail convo. Didn't do this, to keep the subject clean, and also because maybe stacking them all is ideal, or up to individual prefs.

 /cc @dmyung what we discussed was downgraded to just a happy/sad email; long term it might be nice to leverage Jenkins for a nice ChangeLog.