CircleCI : reduced test duration

CircleCI : reduced test duration

Ideally, we want to make CircleCI a "fast" test environment, with short feedback loop (~5mn).
We are still far from this goal.

This patch starts this process by removing "long" tasks which are non-essential and redundant with travisCI.

It also acknowledges that parallelism is broken.
The script should be more heavily updated to support parallelism,
which might be important to support its goal.