tests: Have tests fail when adding veth peer fails.

Before this patch, the test was seen as "skipped" if ip link
was failing.

Signed-off-by: Xavier Simonart <xsimonar@redhat.com>
Signed-off-by: Mark Michelson <mmichels@redhat.com>

tests/system-common-macros.at

@@ -59,7 +59,7 @@ m4_define([ADD_BR], [ovs-vsctl _ADD_BR([$1]) -- $2])
 # The existing 'port' or 'ovs-port' will be removed before new ones are added.
 #
 m4_define([ADD_VETH],
-    [ AT_CHECK([ip link add $1 type veth peer name ovs-$1 || return 77])
+    [ AT_CHECK([ip link add $1 type veth peer name ovs-$1])
       CONFIGURE_VETH_OFFLOADS([$1])
       AT_CHECK([ip link set $1 netns $2])
       AT_CHECK([ip link set dev ovs-$1 up])