MAAS ephemeral boot environments should include the system hostname in /etc/hosts

Due to a bug involving interaction with Juju, MAAS does not currently tell cloud-init to manage /etc/hosts. This prevents Juju charms trying to find our the local IP address from obtaining "127.0.1.1" as the value when looking up the hostname.

However, during ephemeral MAAS boots (such as commissioning, testing, or initial deployment), this can cause large delays during commissioning if the configured DNS server cannot resolve the node, since the DNS request might time out every time `sudo` runs.

Workaround: ephemeral MAAS boots should always execute a command such as this:

    echo "127.0.1.1 $(hostname)" >> /etc/hosts

Note that this should NOT appear in /etc/hosts post-deployment.