Fold file resolver into test resolver.
Fold file resolver into test resolver.

Modify the resolver used by juttle-test-utils, which takes a
collection of modules and falls back to stdlib otherwise, to use the
file resolver as a backup instead of looking under the stdlib
directory itself.

This allows import statements within unit tests to use short names for
stdlib modules if desired. It also allows other test programs (like
the aws unit tests) to also utilize adapter modules.

juttle/juttle