Add env to make_subprocess

Due to a previous commit, a client of make_subprocess is making a call
with an env parameter. As make_subprocess does not have such a
parameter, image upload fails. This patch adds the env keyword argument
to make_subprocess, and use that in the Popen call.

Fixes bug 1216267

Change-Id: I8098b484067b54c15fe95f2bf84c5890db7ebcb3
Merge "Add env to make_subprocess"