Add a utility for listing filtered keys in S3.
Add a utility for listing filtered keys in S3.

Given a "schema" specifying the allowable values for each level
of the S3 directory-like structure, output a list of all the
matching keys on stdout.

sapohl/data-pipeline,mozilla-services/data-pipeline,mreid-moz/data-pipeline,nathwill/data-pipeline,whd/data-pipeline,acmiyaguchi/data-pipeline,acmiyaguchi/data-pipeline,mozilla-services/data-pipeline,nathwill/data-pipeline,whd/data-pipeline,acmiyaguchi/data-pipeline,kparlante/data-pipeline,sapohl/data-pipeline,whd/data-pipeline,acmiyaguchi/data-pipeline,whd/data-pipeline,mreid-moz/data-pipeline,mozilla-services/data-pipeline,sapohl/data-pipeline,mozilla-services/data-pipeline,nathwill/data-pipeline,sapohl/data-pipeline,kparlante/data-pipeline,nathwill/data-pipeline,kparlante/data-pipeline,mreid-moz/data-pipeline,kparlante/data-pipeline