Improve error reporting from appliance

Include the output of the command in the exception
text reported back through the API.

Change-Id: Id437da4b1cbcd29bf5bc7a18cbabfc400fd8e0ba
another test

Change-Id: I740d6a0b7fb42b849991d606f8fc409b3b35aab8
Merge pull request #43 from dhellmann/better-subprocess-errors

Improve error reporting from appliance