Fix "(None)" seed hostname on Debian

The cloud-init package on Debian Linux overwrites the system
hostname to "(None)" unless a hostname is specified in one
of the /etc/cloud/cloud.cfg.d/* files. This change applies
a default hostname of "debian" using cloud-init.

Change-Id: I9b411df44cfa05f899e708900f95719c0bcd6267
Merge "Fix "(None)" seed hostname on Debian"