Bring back the served_model format to the keras materializer

[stefannica]

Describe changes

Restore the previous behaviour of using the saved_model format
instead of H5 in the Keras model materializer. Aside from preserving
backwards compatibility with previous ZenML versions, this also allows
de-materialized Keras models to be served with Seldon (which has no
support for H5).

Pre-requisites

Please ensure you have done the following:

• I have read the CONTRIBUTING.md document.
• If my change requires a change to docs, I have updated the documentation accordingly.
• If I have added an integration, I have updated the integrations table.
• I have added tests to cover my changes.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Other (add details above)

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB

[htahir1]

Ok, sorry that that was breaking

[safoinme]

Legit! sorry that's my bad actually, I didn't consider that Seldon only accepts saved model format instead of hdf5.