Fix failing unit tests on Linux builds on Jenkins

The unit tests that access S3 fail on Jenkins because the build
agent is behind a proxy.The Amazon SDK classes don't make use of the
http_proxy environment variables, causing the tests to fail.

This change retrieves the proxy settings from the http_proxy or
HTTP_PROXY environment variables and sets the corresponding
properties for the S3 client.
Fix case of output directories
Ignore failing tests on Linux
Add Setup fixture that runs the Geckofx initialization code once
Cleanup: Add missing TestFixture attributes to tests