Fall back to default behavior when deployed to a worker node (#593)

* Add test demonstrating failure when running on worker node

* Consider manager status when checking for swarm related features

* Update documentation

test/worker-node/run.sh

@@ -0,0 +1,33 @@
+#!/bin/sh
+
+set -e
+
+cd $(dirname $0)
+. ../util.sh
+current_test=$(basename $(pwd))
+
+export TMP_DIR=$(mktemp -d)
+export LOCAL_DIR=$(mktemp -d)
+
+while [ -z $(docker ps -q -f name=backup) ]; do
+  info "Backup container not ready yet. Retrying."
+  sleep 1
+done
+
+sleep 20
+
+docker exec $(docker ps -q -f name=backup) backup
+
+mkdir -p /archive
+docker cp $(docker ps -q -f name=backup):/archive $LOCAL_DIR
+
+tar -xvf "$LOCAL_DIR/archive/test.tar.gz" -C $TMP_DIR
+if [ ! -f "$TMP_DIR/backup/data/dump.sql" ]; then
+  fail "Could not find file written by pre command."
+fi
+pass "Found expected file."
+
+if [ -f "$TMP_DIR/backup/data/post.txt" ]; then
+  fail "File created in post command was present in backup."
+fi
+pass "Did not find unexpected file."