test: TestNetOverride only needs one --net
test: TestNetOverride only needs one --net

Now that the network loader respects the filename order, --net=all
was causing the default networks to be added as eth0, instead of the
desired custom network

Signed-off-by: Fabio Kung <a5fcd572428ff6f4b84a691712d150785bd20793@gmail.com>

rkt/rkt,coreos/rkt,ybubnov/rkt,joshix/rkt,coreos/rkt,rkt/rkt,Shashwatsh/rkt,kinvolk/rkt,joshix/rkt,alban/rkt,lucasallan/rkt,kinvolk/rkt,lucasallan/rkt,coreos/rkt,joshix/rkt,Shashwatsh/rkt,ybubnov/rkt,kinvolk/rkt,Shashwatsh/rkt,alban/rkt,ybubnov/rkt,alban/rkt,rkt/rkt,joshix/rkt,kinvolk/rkt,lucasallan/rkt,rkt/rkt,lucasallan/rkt