Create the db_redis() task and upgrade redis-server to the one from Chris Lea's PPA, to benefit of REDIS 2.6.12+ SET(nx=…) argument used in 1flow worker locks.
Use the new task for local REDIS installation.
FIX apt upgrade calls.
bump version in __init__.py
Merge branch 'release/2.9.2'
Merge tag 'sparks-2.9.2' into develop

2.9.2