install-server: disable biosdevname on trusty

trusty wants to name devices using Dell's biosdevname (they call it
"consistent naming") in Dell servers and hence the primary embedded
network card would get a name of "em1". This breaks our early_command,
and while we could fix that, it's better to stay consistent with our old
naming for now to help with server reinstalls and other changes across
the board (interface:: definitions etc.).

Set biosdevname=0 in the installer's kernel command-line to revert to
the old behavior per
https://lists.ubuntu.com/archives/ubuntu-devel/2012-August/035670.html

Change-Id: I753123e54df70ce8777c7e08a79fcc4c79f490c9
Merge "install-server: disable biosdevname on trusty" into production