Support multiple paths in input_dir

[jvegreg]

At BSC, we have different paths for variables generated directly from the model and those computed afterwards. In order to be able to read both, we need to pass multiple input_dirs because we need some replacements in the first part of the path.

An example:

EC-EARTH:
  input_dir:
    default:
      - '{expid}/cmorfiles/{activity}/{institute}/{dataset}/{exp}/{ensemble}/{mip}/{short_name}/{grid}/{latestversion}'
      - '{expid}/diags/{activity}/{institute}/{dataset}/{exp}/{ensemble}/{mip}/{short_name}/{grid}/{latestversion}'

Checklist

• PR has a descriptive title for the changelog
• Labels are assigned so they can be used in the changelog
• Code follows the style guide
• Documentation is available for new functionality
• YAML files pass pre-commit or yamllint checks
• Circle/CI tests pass
• Codacy code quality checks pass
• Documentation builds successfully on readthedocs
• Unit tests are available

If you make backwards incompatible changes to the recipe format:

• Update ESMValTool and link the pull request(s) in the description

[sloosvel]

Works fine.