Find containerizer instead of requiring it as an env var
Find containerizer instead of requiring it as an env var

We can now do this because containerizer is now inside gardenwindows instead of
being a separate repo

Signed-off-by: Ben_Moss <80bec717c12290923c80384e0a5fc28cdf75a97e@pivotal.io>

stefanschneider/garden-windows,cloudfoundry-incubator/garden-windows,cloudfoundry/garden-windows,stefanschneider/garden-windows,cloudfoundry/garden-windows,cloudfoundry-incubator/garden-windows,stefanschneider/garden-windows,cloudfoundry-incubator/garden-windows,cloudfoundry/garden-windows