(multinode) Besteffort to disable brnetfilter

- Create the besteffort utility function to run a command
  outside of set -e

- Use besteffort to disable brnetfilter so the gate survives
  when the kernel module isn't loaded.

Change-Id: Ic79aff8cce357d02715a305664ca700e54822627

tools/multi_nodes_gate/airship_gate/lib/config.sh

@@ -134,3 +134,9 @@ join_array() {
   shift
   echo "$*"
 }
+
+besteffort() {
+  set +e
+  $@
+  set -e
+}

tools/multi_nodes_gate/setup_gate.sh

@@ -100,7 +100,7 @@ net.bridge.bridge-nf-call-ip6tables = 0
 net.bridge.bridge-nf-call-iptables = 0
 net.bridge.bridge-nf-call-arptables = 0
 EOF
-sudo sysctl -p /etc/sysctl.d/60-bridge.conf
+besteffort sudo sysctl -p /etc/sysctl.d/60-bridge.conf
 
 if [[ ${REQUIRE_RELOG} -eq 1 ]]; then
     echo