Pass cmd as list, not string, to subprocess.Popen.

When installing debian packages from file i.e.

<pre>
pkg1
  pkg.install:
    - sources:
      - pkg1: salt://module/pkg1.deb
</pre>

cmd is passed as string instead of list to subprocess.Popen, install failing with: 
OSError: [Errno 2] No such file or directory

This was brought up by setting python_shell = False in the cmd.run_all call.