Cleanup dangling sandboxes on boot up

Currently when docker exits ungracefully it may leave
dangling sandboxes which may hold onto precious network
resources. Added checkpoint state for sandboxes which
on boot up will be used to clean up the sandboxes and
network resources.

On bootup the remaining dangling state in the checkpoint
are read and cleaned up before accepting any new
network allocation requests.

Signed-off-by: Jana Radhakrishnan <mrjana@docker.com>

test/integration/dnet/bridge.bats

@@ -30,6 +30,10 @@ function test_single_network_connectivity() {
 	done
     done
 
+    if [ -n "$3" ]; then
+	return
+    fi
+
     # Teardown the container connections and the network
     for i in `seq ${start} ${end}`;
     do
@@ -70,6 +74,27 @@ function test_single_network_connectivity() {
     dnet_cmd $(inst_id2port 1) network rm singlehost
 }
 
+@test "Test bridge network dnet ungraceful restart" {
+    skip_for_circleci
+
+    echo $(docker ps)
+    dnet_cmd $(inst_id2port 1) network create -d bridge singlehost
+
+    for iter in `seq 1 2`;
+    do
+	if [ "$iter" -eq 1 ]; then
+	    test_single_network_connectivity singlehost 3 skip
+	else
+	    test_single_network_connectivity singlehost 3
+	fi
+
+	docker restart dnet-1-bridge
+	sleep 5
+    done
+
+    dnet_cmd $(inst_id2port 1) network rm singlehost
+}
+
 @test "Test multiple bridge networks" {
     skip_for_circleci