Merge tag 'sparks-2.8.9' into develop

2.8.9
Clean the git tree of PYC/PYO files before restarting services, else it can really hurt, cf. http://dev.1flow.net/webapps/obi1flow/group/783/
Avoid getting:

 File "/Users/olive/.virtualenvs/1flow/src/sparks/sparks/fabric/__init__.py", line 127, in execute_or_not
    non_empty = [role for role in roles if env.roledefs[role] != []]
KeyError: 'load'

When typing:

fab test -H obi sdf.restart_services
bump version in __init__.py
Merge branch 'release/2.8.10'