Our functional tests are inherently dependent on 'clouds.yaml' files.
The presence of 'OS_*' environment variables can cause weird test
failures. Simply don't pass them through to our test environment.
Change-Id: I7d24cdff5f1f5798118816b12d7398b87a5f5ed4
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>