Define gateway for default route in $NETWORKS

Define gateway for default route in $NETWORKS

It now goes into one of the ifcfg-eth* files instead of
/etc/sysconfig/network.

NetworkManager in RHEL 7.0 seems to have a horrible bug.  If GATEWAY
is defined in /etc/sysconfig/network and if it brings up the "wrong"
interface first then it adds a host route to the gateway on the
"wrong" network.  This means that outbound traffic is OK.  However,
for incoming traffic, ARP responses go out the "wrong" interface and
are either filtered on the node or are ignored by the host machine.

Signed-off-by: Martin Schwenke <martin@meltin.net>