fix storage_options passing on get schema

[remche]

Trying to discover a catalog on S3 bucket leads to a TypeError : TypeError: get_fs_token_paths() got an unexpected keyword argument 'anon'

plugins:
  source:
    - module: intake_parquet
sources:
  test:
    description: Short example parquet data
    driver: parquet
    args:
      urlpath: s3://bucket/path/file.parquet
      storage_options:
        anon: True
        client_kwargs:
          endpoint_url: https://example.com

This PR fixes the way storage_options are passed to get_fs_token_paths in the same way that builtin CSV plugin.