cli: fix check message command test

* Removes the check from Python 3.

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
cli: tests refactoring

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
cli: using pygit2

* Requires python-dev, libffi-dev and libgit2 packages.

* Requires cffi and pygit2 from PyPI.

Signed-off-by: Yoan Blanc <yoan.blan@cern.ch>
cli: colors for checks

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>