Import OpenHTF reports with missing sections

Test reports in OpenHTF format that were generated by your own tooling rather than by OpenHTF itself could be rejected on upload, and the run was lost.

• Fixed the importer crashing on reports with no log_records or code_info: they now import with no logs and no docstring instead of failing
• Fixed the importer crashing on phases that declare no measurements
• Added a regression test for reports with these sections omitted