Filter out non-requested outputs

[fmigneault]

Description

In contrast to #375, if not all outputs are provided, the results should report only requested ones.
This impacts mostly when response: raw is requested (see #376), since it can make the difference between multipart output vs single output. Furthermore, the response the size can be reduced as well.

In terms of processing execution, Weaver will not omit the creation and storage of those outputs (too complicated considering CWL App Package abstraction), but the job status response could report them partially as requested.

• filter outputs as requested
  • since the CWL might define all outputs as "required", but that the client running the process might be interested in only some of them, filter out the response with only requested ones
  • should the unrequested output files be deleted, or leave them anyway to allow subsequent /jobs/{jobID}/outputs/{outputID} retrieval anyway? Support /results/{id} and /outputs/{id} routes #18
• adjust Resolve transmissionMode handling #377 response content based on number of remaining outputs after filtering, execution mode and response type
• using outputs: {} indicates no-output
  • if the process explicitly defines a CWL with required outputs, this should raise some HTTP error to indicate that the server refuses to run a useless operation
  • if the process doesn't have outputs (a push-update process or something?), or if all outputs are optional (CWL ?), then the operation is allowed
• omitting outputs is equivalent to requesting all outputs
• remove todo in https://github.com/crim-ca/weaver/blob/master/docs/source/processes.rst#execution-body

References

• http://docs.ogc.org/DRAFTS/18-062.html#sc_process_outputs
• http://docs.ogc.org/DRAFTS/18-062.html#sc_execute_response