Merge tag 'sparks-3.7.6' into develop

3.7.6
Implement the --broker_api for flower when using a redis backend as advised in https://github.com/mher/flower/issues/114#issuecomment-22213390 , it works successfully on my development machine.
variable moved.
PEP8 fixes.
bump version in __init__.py
Merge branch 'release/3.7.7'