Fix "environment can only contain strings" errors.
Review Request #7522 — Created July 14, 2015 and submitted — Latest diff uploaded
On Windows hosts, setting things into the environment requires passing in bytes
rather than unicode. Normally I wouldn't really care, but this does also affect
power pack installations.
Ran unit tests. There are a few failures with rbssh, but those were already
present, and are related to the python path.