Needed for make check

This makes us use the correct URL at

   https://source.puri.sm/Librem5/developer.puri.sm/environments/

This needs the protected variables

   - RSYNC_TARGET: remote host and folder
   - SSH_USER: ssh user to log in as
   - SSH_PORT: sshd port on the remote side
   - SSH_KEY: ssh private key
   - SSH_HOST_KEY: ssh host key of target gathered via e.g. ssh-keyscan

filled in to work

Closes: #14

Make sure we do this before each build.