Building mint image fails with minio-py

[Anis Eleuch]

Building a mint image is currently failing with the following message:

You are using pip version 8.1.1, however version 9.0.3 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
The command '/bin/sh -c build/minio-py/install.sh' returned a non-zero code: 1