Add an environment variable to control the creation of eth0/1
interface enablement scripts.
With a tool such as glean, the presence of these scripts will indicate
the interface is configured and configuration-drive settings will not
be applied. This means in a non-dhcp situation like on Rackspace,
network is broken.
On Fedora, where later systemd provides "predictable network interface
names" [1] eth0 & eth1 ironically aren't predictable so this just
confuses things. You really need cloud-init or glean or something to
bring up your interfaces in a sane fashion.
This maintains the status-quo on centos-minimal, but disables creation
for fedora-minimal.
[1] http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/
Change-Id: I3f1ffeb6de3b1f952292a144efab9554f7f99a5f
1f499360fc