Fix CircleCI build

- Specify assert lines for tests to avoid btrfs errors with CircleCI
- Update Docker version to 1.9.1 in CircleCI

test/docker.bats

@@ -105,10 +105,10 @@ function assert_nginxproxy_behaves {
 
 	# Querying the proxy with Host header → 200
 	run curl_container $container /data --header "Host: web1.bats"
-	assert_output "answer from port 81"
+	assert_output -l 0 "answer from port 81"
 
 	run curl_container $container /data --header "Host: web2.bats"
-	assert_output "answer from port 82"
+	assert_output -l 0 "answer from port 82"
 	
 	# Querying the proxy with unknown Host header → 503
 	run curl_container $container /data --header "Host: webFOO.bats" --head

test/multiple-hosts.bats

@@ -32,9 +32,9 @@ function setup {
 
 	# THEN
 	run curl_container $SUT_CONTAINER /data --header 'Host: multiple-hosts-1-A.bats'
-	assert_output "answer from port 80"
+	assert_output -l 0 "answer from port 80"
 
 	# THEN
 	run curl_container $SUT_CONTAINER /data --header 'Host: multiple-hosts-1-B.bats'
-	assert_output "answer from port 80"
+	assert_output -l 0 "answer from port 80"
 }

test/multiple-ports.bats

@@ -52,6 +52,6 @@ function setup {
 function assert_response_is_from_port {
 	local -r port=$1
 	run curl_container $SUT_CONTAINER /data --header "Host: web.bats"
-	assert_output "answer from port $port"
+	assert_output -l 0 "answer from port $port"
 }
 

test/test_helpers.bash

@@ -129,6 +129,6 @@ function prepare_web_container {
 	IFS=$' \t\n' # See https://github.com/sstephenson/bats/issues/89
 	for port in $ports; do
 		run retry 5 1s docker run --rm appropriate/curl --silent --fail http://$(docker_ip $container_name):$port/data
-		assert_output "answer from port $port"
+		assert_output -l 0 "answer from port $port"
 	done
 }