type:string format:binary doesn't work on python-flask (ImportError: No module named binary)

Description

When generating a swagger-server with a model that has type:string format:binary, it completes successfully, but then fail on a missing import.

Swagger-codegen version

tested on both v2.2.3 and v2.3snapshot

Swagger declaration file content or url

https://forge.etsi.org/rep/gitweb.cgi/MEC.GS_012.git/blob_plain/HEAD:/RniAPI.yaml

Command line used for generation

java -jar swagger-codegen-cli.jar generate -o out -i https://forge.etsi.org/rep/gitweb.cgi/MEC.GS_012.git/blob_plain/HEAD:/RniAPI.yaml  -l python-flask -D supportPython2=true

tested with both python3 and python2 support, both stable and unstable versions of codegen.

Current result:

[...snip...]
     from swagger_server.models.cell_id import CellId
   File "swagger_server/models/cell_id.py", line 4, in <module>
     from swagger_server.models.binary import Binary
 ImportError: No module named binary

Suggest a fix/enhancement

Removing the format:binary from the yaml removes the missing import directive. Since import alone [should] do nothing, I don't think removing that import will hurt.

Run the provided generation command and inspect the generated swagger_server/models/cell_id.py import of swagger_server.models.binary. Compare this with the type:string format:binary declaration in RniAPI.yaml. Done means the generated Python Flask server no longer raises ImportError for the binary model while retaining valid model imports.