Updated `OutputStreamConfig` module to enable writing `EventStreamInfo` and `IOVMetaDataContainer`
objects to the output file. Some IOVMetaDataContainer objects are still not copied from input to
output file, so there is still work to be done. This change at least allows the outputs of jobs
configured with `ComponentAccumulator` to be read by diff-root and therefore allow the outputs
to be compared with jobs configured with the old configuration code.

Fix warnings/errors flagged by `flake8`. Mostly unused variables/imports
or stylistic code problems.

Former-commit-id: 640cb4dd

  * Recognise "xAOD" stream type as needing some additional components
    and set these up.
  * This requires merging some property info in AthenaPoolCnvSvc that
    is set up by the PoolReadCfg module, so this property is added
    to UnifyProperties.py.


Former-commit-id: 8343ee95

Walter Lampl authored 6 years ago and Adam Edward Barton committed 6 years ago

Former-commit-id: 0be0dd1a