title: Cannot build bazel 'python_zip_file' filegroup with dependency modules
body: <p>I have a Bazel project where I am trying to package up a python script and its dependencies to install.  <code>filegroup</code>  has a special <code>output_group</code> called <code>&quot;python_zip_file&quot;</code>  which I can use when referencing my <code>py_binary</code> target.  However, that option appears to just zip up the runfiles directory. Looking at the zip file afterwards, all the dependencies (which are stored as symlinks) get dropped. Then when I try to run the zip with python, it cannot import any modules.</p>
  <p>I have no problem running the target using <code>bazel run</code>, because all the module symlinks are present.  Does anyone know how to work around this issue?</p>
  <p>Relevant code from the <code>BUILD</code> file:</p>
  <pre><code>py_binary(
      name = &quot;find_route_tiles&quot;,
      srcs = [&quot;find_route_tiles.py&quot;],
      main = &quot;find_route_tiles.py&quot;,
      deps = [
          &quot;//3rdparty/bazel/pip/fastkml&quot;,
          &quot;//3rdparty/bazel/pip/mercantile&quot;,
          &quot;//3rdparty/bazel/pip/shapely&quot;,
          &quot;//3rdparty/bazel/pip/utm&quot;,
      ], 
      python_version=&quot;PY2&quot;,
  )    
    
  filegroup(
      name = &quot;find_route_tiles_zip&quot;,
      srcs = [&quot;:find_route_tiles&quot;],
      output_group = &quot;python_zip_file&quot;,
  )   
  </code></pre>