installation: Python 2.6 on Travis CI

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
Reviewed-by: Jiří Kunčar <jiri.kuncar@cern.ch>
installation: Flask-Collect to use 0.2.3-dev

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
Reviewed-by: Jiří Kunčar <jiri.kuncar@cern.ch>
access: using unittest2 in Python 2.6

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
Reviewed-by: Jiří Kunčar <jiri.kuncar@cern.ch>
workflows: Python 2.6 compatibility

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
Reviewed-by: Jiří Kunčar <jiri.kuncar@cern.ch>