Q2rCalculation: Add the output_parameters output to the spec (#974)

The `Q2rCalculation` did not declare the `output_parameters` output even
though the `Q2rParser` attaches it always. This would lead to the
calculation excepting because an unknown output would be attached. This
was uncaught by the test because the `Parser.parse_from_node` method
does not automatically validate the outputs. This is because the output
spec that is checked is that of the `calcfunction` (which accepts
anything) and not that of the `Q2rCalculation`.

src/aiida_quantumespresso/calculations/q2r.py

@@ -32,6 +32,7 @@ def define(cls, spec):
  super().define(spec)
  spec.input('parent_folder', valid_type=(orm.RemoteData, orm.FolderData), required=True)
  spec.output('force_constants', valid_type=ForceConstantsData)
+ spec.output('output_parameters', valid_type=orm.Dict)
  spec.exit_code(330, 'ERROR_READING_FORCE_CONSTANTS_FILE',
  message='The force constants file could not be read.')
  # yapf: enable