When gabbi-run is passed one or more files, set the working directory for the associated test suite as the directory of each test file. Doing so ensures that `<@file` syntax in the YAML has a fixed point from which to find the data files. If data comes from STDIN then the test directory is '.' (as it has always been). Fixes #184
Some of the tests in this collection will attempt to connect to google over the internet to validate some behaviors using real socket connections. If this is not desirable (for example behind firewalls or in packaging situations) set GABBI_SKIP_NETWORK to true in the environment running the tests.