IMPROVEMENT: Use Python for the thin shim instead of /bin/sh @thatch45

DO NOT MERGE - for review only @thatch45

This is not complete.  It has only been tested piece-meal and has not
had full integration testing.  I'm hoping for some feedback prior to
completion.

  * /bin/sh is, unfortunately, not very portable
  * Additional commands (tar, md5sum, etc.) are not uniform
  * Python *already* must be there to run salt and is very predictable
    and portable
  * All of the tools necessary to deploy thin are in Python stdlibs