circleci doesn't allow removing containers on the root fs

circle.yml

@@ -3,3 +3,5 @@ machine:
     - docker
   ruby:
     version: ruby-2.2.3
+  environment:
+    circleci: true

spec/simple_spec.rb

@@ -7,7 +7,7 @@ require_relative "support/path_helper"
 RSpec.describe "Simple" do
   before(:all) do
     @debug = true
-    BuildpackBuilder.new(@debug)
+    BuildpackBuilder.new(@debug, ENV['CIRCLECI'])
   end
 
   after do

spec/support/buildpack_builder.rb

@@ -8,8 +8,9 @@ class BuildpackBuilder
 
   TAG = "hone/static:cedar-14"
 
-  def initialize(debug = false)
+  def initialize(debug = false, intermediates = false)
     @debug         = debug
+    @intermediates = intermediates
     @image         = build_image
   end
 
@@ -24,6 +25,6 @@ class BuildpackBuilder
         -> (chunk) { nil }
       end
 
-    Docker::Image.build_from_dir(buildpack_path.to_s, 't' => TAG, 'rm' => true, 'dockerfile' => "spec/support/docker/Dockerfile", &print_output)
+    Docker::Image.build_from_dir(buildpack_path.to_s, 't' => TAG, 'rm' => !@intermediates, 'dockerfile' => "spec/support/docker/Dockerfile", &print_output)
   end
 end