Added a maven_jar reference to JimFS
Added a maven_jar reference to JimFS

This allows tests which access a FileSystem to be completely in-memory. This
will be needed when we have unit tests for Transformations.

Change-Id: I6e4daff87e7b3cd2eff3990efefb9bf3c920aa5b

google/copybara,google/copybara,google/copybara