title: Heroku: Ruby system() commands on java target using multipack
body: <p>On Heroku I want to do</p>
  
  <p>java_controller.rb:</p>
  
  <pre><code>system("java hello");
  </code></pre>
  
  <p>I tried the multipack solution with</p>
  
  <pre><code>heroku config:add BUILDPACK_URL=https://github.com/ddollar/heroku-buildpack-multi.git
  </code></pre>
  
  <p>.buildpacks</p>
  
  <pre><code>https://github.com/heroku/heroku-buildpack-ruby.git
  https://github.com/heroku/heroku-buildpack-java.git
  </code></pre>
  
  <p>And I keep getting    </p>
  
  <p>!     Push rejected, failed to compile Multipack app</p>
  
  <p>when I do a git push heroku master.</p>
  
  <p>This seems like it is due to <code>git clone</code> in multipack compile causing
  error: The requested URL returned error: 400 while accessing https://...
  git --version is 1.7.0</p>