Remove OSX spec options as they do not work

- remove conditionality for macOS (nee OSX)
- add `skip` for tests which are not runnable on macOS
- update README

Author: aramprice

README.md

@@ -177,12 +177,6 @@ cd /opt/bosh/bosh-stemcell
 OS_IMAGE=/opt/bosh/tmp/ubuntu_base_image.tgz bundle exec rake spec:shellout_types
 ```
 
-If on macOS, run:
-
-```shell
-OSX=true OS_IMAGE=/opt/bosh/tmp/ubuntu_base_image.tgz bundle exec rake spec:shellout_types
-```
-
 ### How to run tests for BOSH Linux Stemcell Builder
 
 The BOSH Linux Stemcell Builder code itself can be tested with the following command's:

bosh-stemcell/spec/bosh/stemcell/helpers_sh_spec.rb

@@ -1,6 +1,9 @@
 require 'spec_helper'
 
 context 'helpers.sh' do
+  before do
+    skip "This spec requires linux" unless RUBY_PLATFORM.downcase.include?("linux")
+  end
 
   context 'add_on_exit runs cleanup commands in LIFO order' do
     describe ShelloutTypes::Command.new(

bosh-stemcell/spec/shellout_types/spec_helper.rb

@@ -3,9 +3,16 @@
 require 'shellout_types/chroot'
 require 'tmpdir'
 
+def supported_testing_os?
+  RUBY_PLATFORM.downcase.include?("linux")
+end
 
 RSpec.configure do |config|
   if config.inclusion_filter[:shellout_types]
+    config.before(:suite) do
+      raise "Running 'shellout_types' specs on '#{RUBY_PLATFORM}' is not supported" unless supported_testing_os?
+    end
+
     if ENV['OS_IMAGE']
       @os_image_dir = Dir.mktmpdir('os-image-rspec')
       ShelloutTypes::Chroot.chroot_dir = @os_image_dir
@@ -15,11 +22,7 @@
         Bosh::Core::Shell.new.run("sudo tar zxf #{ENV['OS_IMAGE']} -C #{config.os_image_dir}")
         Bosh::Core::Shell.new.run("sudo chgrp -Rh $(id -g) #{config.os_image_dir}")
         Bosh::Core::Shell.new.run("sudo chmod 775 #{config.os_image_dir}")
-        if ENV['OSX']
-          Bosh::Core::Shell.new.run("sudo chroot #{config.os_image_dir} /bin/bash -c \"useradd  --uid $(id -u) -G nogroup shellout\"")
-        else
-          Bosh::Core::Shell.new.run("sudo chroot #{config.os_image_dir} /bin/bash -c 'useradd -G nogroup shellout'")
-        end
+        Bosh::Core::Shell.new.run("sudo chroot #{config.os_image_dir} /bin/bash -c 'useradd -G nogroup shellout'")
       end
 
       config.after(:suite) do