Exit when launching plugin-v2 if node is not active in Swarm

We retrieve the list of swarm masters for peer discovery when launching
plugin-v2, thus the node should belong to any Swarm when enabling the
plugin.

prog/net-plugin/launch.sh

@@ -16,10 +16,16 @@ echo "Starting launch.sh"
 # Check if the IP range overlaps anything existing on the host
 /usr/bin/weaveutil netcheck $IPALLOC_RANGE weave
 
-# TODO(mp) add wait for swarm
+STATUS=0
+/usr/bin/weaveutil is-swarm-manager 2>/dev/null || STATUS=$?
+if [ $STATUS -eq 0 ]; then
+    IS_SWARM_MANAGER=1
+elif [ $STATUS -eq 20 ]; then
+    echo "Host swarm is not \"active\"; exiting." >&2
+    exit 1
+fi
 
 SWARM_MANAGER_PEERS=$(/usr/bin/weaveutil swarm-manager-peers)
-! /usr/bin/weaveutil is-swarm-manager || IS_SWARM_MANAGER=1
 # Prevent from restoring from a persisted peers list
 rm -f "/restart.sentinel"
 

prog/weaveutil/swarm.go

@@ -2,8 +2,10 @@ package main
 
 import (
 	"fmt"
+	"os"
 	"strings"
 
+	"github.com/docker/docker/api/types/swarm"
 	"github.com/fsouza/go-dockerclient"
 	"github.com/pkg/errors"
 )
@@ -16,6 +18,11 @@ func isSwarmManager(args []string) error {
 		return err
 	}
 
+	// hack-y way to denote that a node does not belong to any swarm
+	if info.Swarm.LocalNodeState != swarm.LocalNodeStateActive {
+		os.Exit(20)
+	}
+
 	if !info.Swarm.ControlAvailable {
 		return fmt.Errorf("node is not a manager")
 	}